Now that's what I call real mountain biking

Riding through lava fields, dodging geysers and battling against winds so fierce you have to pedal hard to go downhill - John Warburton- Lee cycles across South-West Iceland

The bus ride from Keflavik Airport to Mosfellsbaer afforded us our first glimpse of Icelandic scenery. Either side of us lava fields stretched away into the distance, cracked and cratered like the surface of an over-baked loaf. The sky-line was broken by dark, foreboding mountains. With its absence of colour, the scarred landscape was harsh and unwelcoming on this overcast afternoon.

The following morning the Mayor of Mosfellsbaer, together with the local brass band, turned out to see us off at the start of our 400km (250 mile) bicycle tour around South-West Iceland. We cycled eastwards into the sparse volcanic landscape bordered by grey rounded mountains and yellow rhyolite (a form of granite) peaks.

The first 30km took us to the edge of a huge volcanic chasm overlooking the Thingvellir Plains. Here, the two tectonic plates on which Iceland sits are slowly pulling the island apart. In 930 AD, the Althing, or parliament, was established on the edge of these plains. For the next 800 years the clan chiefs met here each year to take the decisions that would govern the nation. The Althing adopted Christianity in 1000 but it did little to reduce the bloody feuds and harsh punishment meted out, as witnessed by the nearby Drowning Pool into which women who had committed adultery were jettisoned, tied up in sacks.

We woke on the second day to bright sunshine and the sound of snipe swooping and diving above our tents. A stage on asphalt had us whizzing along towards Geysir. Our Icelandic guide, Halldor Bjarnason, who had already adopted the role of father of the group, told me with a twinkle that the original Great Geysir, from which all geysers around the world had taken their name, was now impotent, like an old man. We watched as its successor, Strokkur, bubbled and boiled, building up a head of steam until with a final roar it shot a column of water 70ft into the air.

We stopped for lunch beside one of Iceland's most remarkable sights - Gullfoss, the Golden Waterfall. Here, the River Hvita plummets over 100ft down broad, two-tiered falls before disappearing into a sheer sided gorge. Turning southwards we entered an upland farming area. The green fields and red roofs of the farmhouses stood out in colourful contrast to the dark hills, but in this area even these seemed lighter.

The farms were scattered sparsely. Iceland's population is only 250,000 and roughly half of these people live in Reykjavik, so there is no shortage of space. The farms have little cultivable land. In the few fields, grass is short and coarse with limited top soil. Erosion is a major problem. Many of the farms raise their crops intensively under large glass houses, taking advantage of the geothermal energy provided by the many hot springs for heating.

Our third day was to be the big one: a total of 100km from Arnes to Hella including a long, hard off-road section. We began in low cloud, swooping down a long incline to the side of the Thjorsa River, Iceland's largest, drinking in inspiring views away to the glistening snow-covered flanks of Mount Hekla in the distance. We left the road at Hjalparfoss, another magnificent cascade of water, and the rough dirt track became a writhing snake, twisting its way up and down hill through the rough lava flows. This was off-road biking at its best - or a nightmare on earth, depending how much you enjoy fighting through soft sand, along dried streambeds, up steep hills and through small boulder fields.

We emerged onto a barren plain that leads under the flank of Mount Hekla, an active volcano that erupts regularly without warning - the last time was 1991. Medieval mythology held it to be the gateway to hell. Pedalling into the face of a strong headwind, through the debris of previous eruptions and unsure whether 1997 was going to be the date of the next hail of molten lava, this description struck a deep chord.

Starting the westward leg of our journey the following morning we got a taste of Iceland's infamous weather. Huddled in woollen hats and waterproofs we set off into the face of northerly gales and driving hail. The powerful crosswind meant that we had to lean our bicycles at a perilous angle merely to prevent being blown over. When the track turned directly into the wind it became a battle of endurance to force the bicycle onwards. At one point I found myself pedalling with all my strength to bike go forward even though I was heading down a relatively steep hill.

Mid-morning, we turned off onto a side road and suddenly the wind was behind us, chasing us along at breakneck speed. The relief, and the exhilaration of speeding was close to ecstasy. The wind speed had risen to 42mph. Finally we were stopped by our advance vehicle party who said that the road ahead was impassable. On crossing a bridge a few miles ahead, their truck had been severely buffeted by the wind. When they had got out they had been unable to stand without holding onto the vehicle and the resulting sandstorm had begun to strip the paintwork. No place for a cyclist.

Our final day's journey back to Reykjavik summed up the Iceland experience. We cycled past long mountains down to the sea where we were surrounded by flocks of mobbing Arctic terns. In the lee of an extended cliff line we sped along in the sunshine until we turned for the interior once again, climbing up through a series of lava fields to volcanic craters and lakes. At Krisuvik we came to an area of bubbling geysers and a fierce steam vent shooting boiling water and clouds of steam into the air in an unending stream. The lava fields vary from relative smoothness, carpeted in a grey- green bed of deep spongy moss, to a dark, Dante-esque landscape of broken lava, frozen into the weirdest shapes. Plates of rock stick up at crazy angles. The craters of mini-volcanos appear frozen in time like pustules of larva caught and solidified at the point of explosion.

The scenery of Iceland is magnificent. Much of it is not obviously beautiful, more starkly impressive - windswept, austere and at times almost overpowering in its desolate barrenness. The only relief is provided by patches of lichen and tiny clumps of ground-hugging flowers, clinging perilously to an occasional turf.

As we approached Reykjavik we passed through a beautiful valley ablaze with blue Alaskan lupins. Fishermen had waded out into a small lake and were fly casting for trout. For our group of telephonists, bankers, doctors, insurance brokers, teachers, and nurses it signalled the end of a great challenge, for many the severest physical test they had ever faced. Aside from the enjoyment - the outstanding scenery, the warm hospitality, the esprit de corps - our satisfaction was knowing that in taking part, the Macmillan Cancer Relief fund had raised well in excess of pounds 100,000.

Season

The Icelandic summer is extremely short. The compensation is that in the period around Midsummer Eve there is perpetual daylight. But the weather is never reliable, and you need to be prepared for high winds, rain, and possibly hail.

Expense

The only things that are free in Iceland are the weather, the scenery, the wildlife and the space to enjoy them. Everything else is extremely expensive. As a yardstick, a beer in a bar in Reykjavik will set you back the equivalent of pounds 5.

Adventure programmes in Iceland: For those wanting to take part in trekking, biking, ski touring, snowmobiling, vehicle touring, and sight seeing contact Halldor Bjarnason of Iceland Safari Travel (Tel: 354 562 4222) or cycle tour specialist Halldor Garoarsson of Blue Biking (Tel: 354 565 2089).

Macmillan Cancer Relief Challenges: As part of its fund-raising, Macmillan Cancer Relief organises a series of events for active people who seek a challenge and want to raise money for the charity. Later this year there will be a white water challenge in the French Alps, and a bicycle tour and trek in the High Atlas Mountains of Morocco. A similar programme of challenges is planned for next year. For further information contact Katherine Norman or Pippa Faithful (Tel: 0171 887 8288/8225).