The Myvatn area
Myvatn (translated Mosquito water) is the 2nd largest lake in Iceland. It is famous for it's fantastic birding and good salmon fishing. More than 20 duck species and many other birds breed here every summer. I didn't take any lenses suitable for bird photography and so you have to excuse, that I just talk about it.
But there are many other places worth visiting, for example the Hverfjoll, a large Explosion crater (above)
or how would you like to visit the Krafla, a very active fissure volcano, which erupted the last time 21 years ago?
And if all this is not enough, there are interesting Lava formations at the Dimuborgir and the Namafjall, with its hot mud pots.