Þingvellir is a region just outside of Reykjavik, and sometimes overlooked by travelers set on exploring the golden circle. Þingvellir circles around a large lake and has some amazing views. I recommend driving around the full length of the lake. There are many drop offs and hiking bases along the road. Just off the northern tip of the lake there is a hike you can take down a valley where they filmed a few episodes of Game of Thrones. My favorite part of the drive was all the farms we past filled with Icelandic horses.