Before dawn I started climbing Croaghaun (Cruachán) mountain at the westernmost end of Achill. Rain and mist and cloud and sunshine came and went, making ever more beautiful views in the changing light. Croaghan is a long hike (or was for me as I stopped every ten metres to set up my tripod!) but the top has to be one of a best summits in Ireland. The southerly slope rises steadily to 664m, and then the whole mountain falls into the sea 2000 feet below. These are the highest cliffs in Ireland and second highest in Europe. The abruptness of the drop, the fact that one comes on it so suddenly and the views that it commands all make this a very, very worthwhile hike. It is breathtaking.

From the summit one can hike south west along the cliff edge and, if feeling energetic, re-ascend and hike the cliffs back to Keem beach. But there being so much to see, and this two hour hike having taken me five already, I said goodbye to the sea cliffs and turned for the car and an early afternoon breakfast that I was badly in need of.

I re-joined the mainland at Mulranny, on the southwestern end of the Nephin Beg mountains. Here I found a tiny glade of Scots pine, some stunning hawthorns in full fruit, and a deeply attractive range of mountains. The Nephins stretch north and east from here in what I think I must be one of the longest stretches of uninterrupted mountainscape in Ireland. No roads penetrate this region and I think one could probably hike for twenty kilometres or more without crossing one. That's not much for those countries with big wilderness areas but if you've visited Ireland you'll know that there are tiny roads everywhere, and that is actually pretty rare to find oneself more than say a mile from some sort of road.

Vast, isolated areas have a dangerous fascination for on me, urging me out of the car and up the nearest ridge. Reason, and tired feet from the morning's roamings prevailed and I settled for reconnaissance instead. I drove the Nephin Drive, a little road winding up the parallel to the east side of the range with great views of lakes and mountains.

I camped there that night and made plans for a long hike the next day. Rain woke me in the night and in the morning the prospect of a two day trek across a windswept mountain range in the driving rain looked a lot less appealling than on the previous sunny evening. Instead I headed north, picking roads at semi-random, going to places that looked interesting on the map and finding they weren't, and vice versa. I found another magnificent hawthorn and while photographing it discovered some old apple trees around a derelict cottage and feasting on some of the best apples I've ever eaten.

Scanning the map for points of interest in the area, I noticed Errew Abbey on the edge of Lough Conn. The Augustinian abbey dates back to the 13th century, and was built beside an earlier oratory, the wonderfully named: Tempeallnagcallaighdoo, or: the temple of the black nuns. Errew comes from the Irish word Oireadh, meaning the tilled land. I liked this remote outpost, the thought of monks growing their crops on the peninsula and painstakingly carving the delicate windows, arches and columns of their abbey.

A room adjoining their cloister is piled with assorted carved stones that the Office of Public Works couldn't find a home for when they took over care of the ruined abbey. My eye was caught by a fragment of a circular cross that someone had been using as a seat while they drank bottles of beer. I've carved stone; it takes a very, very long time to make any significant progress. If you ever get a chance to try stone carving, do so. It will completely change the way you view any stone building. Errew abbey affected me deeply, reminding me of the transience of all our great endeavours, and how easy it is for us to forget the fragility of all empires.

The weather worsened as the day wore on, developing into a full gale complete with driving rain by mid-afternoon. I was very glad not be high up on a ridge in the Nephins, many miles walk from the nearest road. I wound my way through the towns of north Mayo: Crossmolina, Ballina and Killala. I visited a great Bronze Age standing stone that had been carved with Ogham writing in the 5th century AD by a local king; a 4000 year old monument graffitied 1500 years ago with the name of a king no-one has remembered for a millenium.

At the coast the beaches and cliffs were being pounded by an Atlantic gale, a state of affairs not unfamiliar to them and likely to persist for the next seven or eight months. I wandered westwards, past the Céide Fields where field systems more than 5000 years old were discovered beneath what is now blanket bog. There is a suggestion that these first settlers may have contributed to their own downfall, clearing the existing forest to create arable land, which then resulted in rainfall leaching the soil and the formation of the blanket bogs. I think about this often as I travel through Mayo - what did it look like when it was forested? Could it ever be forested again?

I guess that depends on one's definition of 'again'. If I'm thinking in terms of my lifetime then it seems unlikely. However on geological scales, then the answer is almost certainly yes. This area of Ireland was under glaciers 10,000 years ago, pine forest 4,500 years ago during a period of milder and drier climatic conditions, and then bog formation continued again 500 years later as the climate became wetter. When I see sinewy ash and holly trees clinging to the wet cliffs and gullies of the mountains around here I am reminded about the sheer, bloody persistence of life in all its forms, and that if conditions make it possible for trees to take hold again in the west of Ireland then they certainly will, whether we're there to witness it or not.

On to Rossport, where Shell are in the process of building a natural gas refinery and bring a pipeline ashore from the undersea gas fields to the west against serious local opposition. People are upset and angry and protest daily. There are claims that all mobile phone calls made in the area are tapped; that locals are videoed by the private security firm protecting the site. I don't know enough about the issue to comment on it, but you can look up Rossport Mayo on Google and see what you think, and journalist Fintan O'Toole's article on the heavy-handedness with which the State are dealing with this makes some interesting points. And despite this there is good humour and welcome and a whiskey pressed on me when I stop at a local pub to buy Taytos. The whole length of the west coast is a tough place to live year round: over 200 days of rain a year, persistent westerly winds, marginal land for agriculture - and yet there is always this good humour, wit and welcome. Long may it last.

Bad weather and brooding over corporate ethics makes me uncomfortable with staying in the area that night, so I drive south in tunnels of rain and darkness lit by lines of cat's eyes, south to Roonagh where the ferry leaves for Clare Island in the morning. In search of a beach to camp on I nearly drive over a small cliff into the sea and decide instead to camp in the car, rocked to sleep by the buffeting of an Atlantic gale.

I sleep amazing well (considering the smallness of my car's back seat) and wake in the pre-dawn. One glance is enough to tell me there will be no ferries sailing today. Instead I explore the coastline west of Mweelrea, where I find sheep walking along the beach and a scattering of empty holiday homes where I'm fairly sure there were none ten years ago. The old farms are huddled and tucked, everything here has its back to the wind. The new homes look forlorn; sightless windows looking west, no cars parked, no children - there is a feeling that there is no-one here, nor will there be until next summer. I feel that these houses are cast up by an unusually high economic tide which will leave them derelict if, or perhaps when, it recedes.

The weather suggests a retreat inland, so I drive eastwards intending to cut back through Doo Lough and pass north of Ben Gorm to head to east Mayo with it lakes and plains. However as I drive down towards the lake I notice a huge waterfall coming down the mountainside, one that wasn't there a few days ago. Nothing for it but put the camera gear in a waterproof bag and head off across the bog to photograph this spectacular cascade that I can hear roaring from a mile away. It's only 11am, can't take more than an hour...

Halfway across the whole bog is shifting and rocking beneath my feet and I'm starting to think that maybe this was a very bad idea. There are visible ripples in the surface extending several metres around me. Now stories abound in Ireland of unwary people who came to sticky ends in bogs like this, stories I had always dismissed as highly unlikely. Until now. I make a lunge with my right leg for a firmer looking tussock, which immediately plunges my left leg through the thin surface of the bog and knee-deep in icky decomposed vegetable matter. Moving with a swiftness that surprised even me, I extract my leg and make it onto the tussock and squelch around considering my options. Going on looks no worse than going back so I press on, in a mixture of false bravery and genuine stupidity.

The waterfall is as spectacular up close as it promised to be. We have a long photo shoot, me not having worked with a big waterfall before. And then it's just too interesting out here to go back. I try to cross the cascade and end up climbing half way up the mountain before I find somewhere narrow enough to risk jumping. (A few years back I destroyed a very nice camera and two very, very nice lenses by falling into a river, so now I'm a little cautious around running water.)

Even though it's raining intermittently I'm dressed for it, warm(ish) and dry(ish), except for one boot, and the mountain just gets better and better. I find another river that has cut a deep gully in the mountainside. Hardy native trees have taken advantage of the shelter, and it is like a little Irish arboretum: ash, holly, oak, rowan and hawthorn are all here.

More hiking brings me to the vast corrie on the northeast side of the Mweelrea group, under Ben Bury. It looks like some giant from Celtic pre-history has taken an icecream scoop and spooned out a huge chunk of mountainside. The cliffs at the back disappear up into the clouds and must be easily a thousand feet high, maybe much more. Numerous waterfalls stream down the cliffs, looking like white threads from the ground. There are immense scree slopes with huge boulders at their feet, here and there dotted with soggy sheep. By now my one hour sortie has turned into a five hour trek, but it is worth it. The colours, though muted, are spectacular and it feels right to be ending journey nearly back where I started four days earlier.

I walk back towards the road, following some old vehicle tracks. I know there is now a biggish river between me and the road, but I reason that if a vehicle (whatever it was) got in here there must be a bridge, right? Wrong. I look at this final obstacle and consider just how big a detour will be required to get around it. It is five o'clock. And then I realise that my feet have been wet for the last three hours anyway, so I wade through and squelch back to the car and a (very) late breakfast and head for home.

Ralph Doyle