Tröllafoss Waterfall

Tröllafoss is a little-known waterfall in the Leirvogsá river, in the Mosfellsdalur area north-east of Reykjavík. The river drops into a compact gorge below the old Stardalur volcanic landscape, creating a darker, wilder-feeling stop than its short distance from the capital suggests. It is a rewarding choice for visitors who enjoy local nature, geology and a quieter walk rather than a large visitor site.

Do not confuse this Tröllafoss with the similarly named Tröllafossar in Borgarfjörður. This guide is for the waterfall in Leirvogsá near Mosfellsdalur, where the river runs through the remains of an ancient volcanic system before cutting through the gorge at Tröllalágar.

Quick guide to Tröllafoss

A waterfall inside an ancient volcanic landscape

Tröllafoss is more than a short cascade. The Leirvogsá flows through Stardalur, an area associated with the deeply eroded remains of an old central volcano. At the waterfall, the river drops between rock walls into a gorge it has carved through the Tröllalágar area. This geology gives the site its close, enclosed character and explains why the waterfall feels more secluded than many capital-region stops.

Take time to look at the rock as well as the falling water. The gorge, river channel and surrounding slopes are the story. The site is recognised for its geological value, so keep to durable ground and do not remove stones, disturb vegetation or descend into the ravine for a photograph.

Finding Tröllafoss responsibly

Tröllafoss is reached through a rural part of Mosfellsdalur rather than a formal visitor centre. The approach has changed over time, and paths can be muddy, narrow or uneven. Use current mapping and local signage, park only where it is clearly permitted and never block a farm road, gate or passing place. If access is unclear, choose not to continue.

This is not the right place for a hurried roadside stop. Allow enough daylight to walk back without rushing, tell someone where you are going if you are travelling alone and turn around if wind, rain or poor footing makes the route feel unsafe. Respect for local land and the river is what keeps a low-key place like this visitable.

A quiet alternative near Reykjavík

For travellers based in Reykjavík, Tröllafoss can be a refreshing change from busy signature sights. It suits a relaxed half-day built around the Mosfellsdalur countryside, and it can be combined with a visit to Helgufoss if the route, weather and access conditions make sense. Do not plan this as a checklist of waterfalls; the roads and paths reward a slower pace.

The falls are most approachable when the ground is dry and daylight is generous. After heavy rain, the river and paths can be more dramatic but also more hazardous. In winter, snow, ice and short days make this a much more specialised outing; choose a more accessible waterfall unless you have current local knowledge and appropriate equipment.

Photography and safety at the gorge

A wide lens can capture the waterfall and enclosing gorge, while a longer lens is useful for keeping a safe distance from water and edges. The best image is often made from the path, using the river’s curve and dark rock to frame the fall. Do not climb down loose banks, cross the river or step onto undercut ground for a closer angle.

Leave the place quiet. Keep voices low, pack out all rubbish, avoid drones unless they are clearly permitted and give wildlife and other visitors space. Tröllafoss is valuable precisely because it still feels like a small piece of countryside close to the city.

Tröllafoss FAQ