At the head of Hvalfjörður, and up Botnsdalur valley, lies Glymur, Iceland’s highest waterfall (198m). From the trailhead, it’ll take a couple of hours to reach the cascade's viewpoints on rough, slippery trails. A log is placed to bridge the river only in summer. At the trailhead there's a good map with instructions. Reach the trailhead by following the turn-off on Rte 47 to Botnsdalur.
Bring water shoes for fording the river, if you plan to cross and return on the west side, or retrace your steps on the east side. Try to visit after heavy rains or snow-melt for full effect. Note: there is no camping allowed around the trailhead.