Mount Keilir is a small volcanic mountain to the southwest of Hafnarfjörður. It can be easily visited when travelling between Reykjavík and Keflavík Airport, or the Blue Lagoon.
The mountain was formed during the Ice Age, underneath a glacier and is classed as a hyaloclastite mountain, although scientists believe it to actually be the plug of a large crater. Hikers enjoy climbing the mountain as it's not too high, but still poses enough of a challenge. Once you climb to the top, which takes around 2-3 hours, you are rewarded with a beautiful 360-degree view that simply takes your breath away.
It takes about 25 minutes to drive from Hafnarfjörður city centre to Keilir. You simply drive towards Keflavík International Airport on Reykjanesbraut and follow the signs for Keilir.