Vatnajökull is the biggest ice cap in Europe by volume, a white plateau covering about eight percent of Iceland, with outlet glaciers that spill into valleys and lagoons. Beneath the ice lie volcanoes, including Grímsvötn and Bárðarbunga, that erupt from time to time, melting the ice from below and sending floods of water down the rivers. The national park that surrounds it, one of the largest in Europe, is a place where fire and ice are visibly at work on the same ground.
The nearest place with fuel is far away, at Mývatn or Egilsstaðir, and the tracks that lead here are rough mountain roads, marked with an F on the map, which cross rivers without bridges. Such routes are usually open only for a few weeks in midsummer, and the conditions change with the weather, so anyone planning to go should check road reports and travel with someone experienced.
From the Ring Road, the ice cap can be seen as a white line above the farms, and the best roadside views are on the south coast, where outlet glaciers come down almost to the sea, and icebergs float in lagoons. The mountain of Öræfajökull, rising to over two thousand metres, is the highest in Iceland. The riding, on the paved Ring Road, is wide open, with far horizons, and the wind can be fierce.
The summer months are the only practical time, and even then the weather is unpredictable, with rain, fog and cold. Carry warm and waterproof clothing, food and water, and tell someone your plan. The reward is a landscape on a primal scale, black sand, blue ice and grey sky, which makes the human world seem very small indeed.