Brúarfoss is also called the blue waterfall and means «bridge over waterfall». The river Brúará flows down over 2-3 meter and ends in a U shape slot. The waterfall is very photogenic because of this shape and the blue color of the water.
Take road 1 up to Mosfellsbær. Turn into road 36 to Þingvellir. From there take road 365 to Laugarvatn and in addition take road 37 in the direction to the Geysir. About 2-3 kilometer after you crossed road 355 you will cross the river Brúará. Here you can also find a small parking. Walking upstream brings you to Hlauptungufoss and Brúarfoss. The trail is a bit muddy at places when it rains but the walk is quite easy. Between Brúarfoss and Hlauptungufoss there is another small waterfall called Miðfoss.
The walk takes appr 45 minutes and is 3,5-4 kilometer long. If you have trouble finding Brúarfoss, David Britnell made a youtube video with instructions here!
Brúarfoss derives its name from a natural stone arch over the river near the waterfall in earlier times. The story goes that an employee of the diocese Skálholt destroyed the bridge in 1602 when there was great famine in Iceland. He wanted to keep away the hungry passants who came to Skálholt for food. Some time later, the man drowned himself in the river.