Dettifoss is not the highest waterfall in Iceland, but it is the most powerful in Europe by volume, and standing next to it you quickly believe the claim. The glacial river Jökulsá á Fjöllum, grey with silt, tips over a rim about a hundred metres wide and drops some forty-five metres into a canyon, sending up a cloud of spray that hangs over the plateau and soaks anyone who gets too close. The noise is a constant roar, and the ground trembles slightly under your boots.
The country around it is a different sort of Iceland from the postcards. This is a high, stony desert of black basalt, moss and scree, with few trees and a wide sky. The river runs through a canyon cut into the rock, and a little way upstream and downstream there are two more falls, Selfoss and Hafragilsfoss, each with its own character. It was here that the opening scenes of the film Prometheus were shot, and it is easy to see why a film-maker would pick a place that looks like the start of the world.
Riding to Dettifoss involves a choice. The western approach, on route 862, is now paved and the easy option, with a smooth ride and big views over the plateau. The eastern side, on route 864, is a gravel road with potholes, washboard and loose stone that can be tricky on a road bike and demanding on any bike when it rains. It is also closed in winter. Check conditions with local information before you commit, and be careful of wind and fog, which can make the plateau a cold and disorienting place. Even in summer you will want a warm jacket.
The nearest pumps are around Mývatn to the west and in Húsavík to the north, so fill up before you go, and bring food and water if you can. A basic facility with a toilet is usually available at the car park, and in season there may be a small kiosk.
Stay on the marked paths, because the rocks are slippery and the drop is serious. The best time to come is a dry day in summer, when the light and the spray often make a rainbow across the canyon, and early or late hours keep the crowd to a minimum.