I really liked the geysers, especially this one which shot out of a pool (as opposed to a cone).
Another kind of geothermal feature are these pools of hot water. In this one as the water cools towards the edges different kinds of bacteria and algae live, making the different colors.
This is an example of a terrace, where the water flows down leaving interesting shapes. Again, it can be different temperatures and therefore different colors. When the water stops in a given area, it turns grey but the shapes are still interesting.
Another variation on the terrace theme.
Here is a pool of reddish mud which is getting shot into the air now and again.