You should drive there by yourself. Note, that only 4×4 vehicles are allowed to make the journey! The other option is to jump into one of the jeeps or mountain buses that drive daily into Thorsmork. These jeeps and buses are in operation from May to October, departing from Reykjavik.

Kerid Crater
The easiest way to get there is to drive there yourself. The crater is located along the Golden Circle route