Helgafell
Helgafell is the holy mountain that figured so prominently in Icelandic history and literature. In reality, it's a 73m (240ft) hill, yet it apparently still retains some of its magic, and those who follow a few simple rules while climbing it are entitled to have three wishes granted. First, you must climb the southwest slope to the temple ruins without speaking or glancing backwards. Second, the wishes must be for good and made with a guileless heart. Third, you must descend the eastern slope and never reveal your wishes to anyone. Helgafell is 5km (3mi) south of Stykkishólmur, in West Iceland.

(From Lonely Planet Guide.)

Note that there are several places of the same name, including the volcanic cone on Heimaey. This particular one, however, is near Stykkishólmur.