From August 2007: You can stop by Keriš Crater along the way to Gullfoss and Geysir from Hveragerši or Selfoss. The parking is signposted and is right next to the top of the crater.
From August 2007: Hveragerši Geothermal Area is in the middle of Hveragerši. You can see several hot springs and fumaroles. If you are lucky you can see one of the springs bubble up, which I was told happens only once a day.
From August 2007: Do a day trip driving around the "Golden Circle". We stayed overnights in Hveragerši, started driving around 9:30am and got back to Selfoss around 5:30pm. Total driving time was about 3 1/2 hours, so we had plenty of time for each stop including some hiking. One of the roads was unpaved, but our small rental car was fine, no need for 4x4. See separate tips on each of the following places we stopped that day:
This huge mountain is situated just outside Selfoss. This is a huge and impressive mountain. If you want, you can drive partly around it. It is really nice to see the different kind of shades. Especially when there are clouds and sun.
When you are in Selfoss, you can walk along the river Olfus. This river is massive. And there is a strong current in this river. You will have nice views to the other side of the river.