Some companys that offer Tours near Klaustur are:

Secret Iceland offer tours to Laki during the summer, and to Fagrifoss and Fjaðrárgljúfur, all the year around. Also they offer Private Northern Lights Hunt in a Super Jeep from Reykjavík during the winter

Iceland Bike Farm is the first and only natural bike park in Iceland

Icelandic Mountain Guides offer many options of hiking tourst

Reykjavík Excursions provides many tours in Iceland