Next to the ringroad of lake Myvatn there was a lava formation on the lakeside. We did a very short walk to have a proper look.
As we had seen the things we wanted to see in the Myvatn area we decided to clim up the Krafla mountain/volcano. There were many other things to see, but they weren't interesting for us or it wouldn't be wise to do it together with my wife that was 27 weeks pregnant. Walking up Krafla was very steep, but we took it slow and got a very nice view over the Krafla region.