The highlight of our trip was definitely Volcantours
We did 4 different tours during our one-week stay in Iceland (Golden Circle, Walk on the Glacier, Snorkling in Silfra) and the highlight of our trip was definitely this new tour with a company called Volcantours (www.volcanotours.is). We were the 13th and 14th participants in the tour and we totally loved it! We toured around the Reykjanes peninsula where we saw stunning landscapes, lava fields, hot springs and went into caves and even inside a volcano. This is not a crowded bus but a super jeep and we were only my friend and I so it was personalized to what we wanted to see. They lended us all the necessary gear for caving (which you don't have to do if you don't want to). The company is based in Grindavik, but they'll come pick you up wherever you are in Reykjavik. The guide knows the area inside out. He knew where to take us and knew where the best picture spots were. Price is 17000 KR but is fully worth it.