Þeistareykir is a somewhat remote high-temperature geothermal region, located in northeast Iceland, between lake Mývatn in the south and the city of Húsavík in the northwest. Central volcano is Þeistareykjabunga.
Only unpaved roads lead to Þeistareykir. On top of that it is not part of commercial tourist tours. That may be the reasons for being still an insiders tip. Most of the time you will be there on your own. Basically there are three routes available to reach the area, one starting in Húsavík and another two branching off to the east from the unpaved section of road 87. Although convenient, in reasonably good weather none of the roads really require a four wheel drive, if you drive carefully. With a normal car in poor weather the road from Húsavík should be preferred, since it is also the truck route. Þeistareykir is an area of exploration and use of geothermal energy, so be prepared to find related activities on location.
Geothermal features extend over a quite large area submontane Mt. Bæjarfjall, bordered by the Ketilfjall ridge in the east and the lava plain Þeistareykjarhraun in the west. The main road separates two geothermal areas, Þeistareykir (shares the name with the whole region) in the east and Hitur in the west. Most eye-catching is Hiturs muddy-blue collecting lake northwest of Mt. Bæjarfjall. It has developed in 2007 as a result of discharging outlet water of geothermal drilling, and is extending since then.
For better orientation I divide the thermal features into six groups: Ketilfjall Group near Ketilfjall ridge, Bóndhólsskarð Group in the depression between Ketilfjall and Mt. Bæjarfjall, Hillside Group on the north slope of Mt. Bæjarfjall, Þeistareykjargrundir Group on the plain north of Mt. Bæjarfjall and Painted Creek Group in and above the creek near Þeistareykir hut. All are part of Þeistareykir geothermal area. Hitur geothermal area comprises among others the Tjarnarás Group on the plain northwest of Mt. Bæjarfjall and west of the road. Of course, some groups may not be composed in a scientific sense, but it seems to be appropriate to describe the features and to rediscover them later on location.
Please note that the thermal areas of Þeistareykir are potentially dangerous, not developed for tourists, that neither signs nor boardwalks are available and you have to take care of your own.