The first tour I went on in Iceland was the Golden Circle tour. It takes one to a few main sites:
Gullfoss:
the geothermal area with Geysir (inactive) and Strokkur:
and the Mid-Atlantic Ridge (this is the boundary of the American tectonic plate, the flag shows where the Althing was held (the Althing is the longest existing parliament in the world)):
To be continued.