Glymur is the second-highest waterfall in Iceland, with a cascade of 198 m. It was long regarded as the tallest until being surpassed by Morsárfoss, a newly measured waterfall near Morsárjökull in 2011.
It is situated at the rear end of the Hvalfjörður. Since the opening of the Hvalfjörður Tunnel under this fjord, visitor numbers have dropped.
The river Botnsá runs from the Hvalvatn lake and after a short distance the water falls down alongside the Hvalfell mountain into a steep canyon. The waterfall can be accessed from a parking area at the end of the road. Hikers can view the waterfall from marked paths on the east side of the river Botnsá.