This loop makes for great running terrain around the Blue Lagoon area. The footing is mixed rocks, footpath, mossy surfaces, etc.
The run starts at the parking lot for the Blue Lagoon facilities, just left of the bus waiting building.
I was a bit worried at the start, about some signs saying there's no access, but I believe these were about danger of entering the hot springs. Other than that, the trail was easy to navigate. There are cairns, and some wooden poles marking the route.