In many places you can see structures of stone. Many, if not all, of them were created by volcanic activity. Especially basalt is easy to recognize because of its characteristic shape: (usually) hexagonal pillars.
You can find similar remains in several parts of the earth. These pillars occur, because of the certain environmental conditions while cooling down of the lava.
At the southern coast of Iceland near Vik (and probably in other parts of our planet, too) you can find huge caverns, where you can even see these pillars from below. These pillars have a side-lenght of approximately 30 – 40 cm. So, you can easily use the lower ones as a seat.