Nikulásargjá/Flosagjá is amongst the main faults at Þingvellir national park. This fault and the faults leading from it marked the east side of the old assembly site. The other limits were Lake Þingvallavatn in the south, the higher wall of Almannagjá fault in the west and Kastalar (two lava hills) in the north. Within these boundaries, men were free to take part in the proceedings of the Althing that assembled at this site from the year 930 - 1798.

The name Nikulásargjá is derived from when the District Commissioner Nikulás Magnússon drowned himself in Flosagjá during a summer night in 1742. Ever since then, the eastern branch has been known as Nikulásargjá. The water is up to 25 metres deep, 3-4° Celcius and very clear.

When the gorge was bridged in 1907 people startet throwing coins into the water below and so, this part of the fault became known as Peningjagjá (Money fault). Throw in a coin, make a wish and if you can see it hit bottom some say your wish will come true.

The water filled faults at Þingvellir national park make a unique spot for scuba diving and are popular as such.