Most activities in Rotorua involved the many geysers/hot pools situated in the region. Rotorua alone produces 15% of New Zealand's power, just from geothermal energy. Just walking around the area you can find several bubbling mud pools. Unfortaneatly all of the hot gasses bubbling through the pools causes the area to smell like rotten eggs from all of the Sulphur. Our hostel pool was geothermally heated which made it pleasantly warm to swim in.
Both Rotorua and Taupo had huge lakes surrounded by mountains which made them really picturesque and Taupo's lake is actually a supervolcano that erupted around 180 AD and cooled the earth for 7 years afterwards. There was a free hot springs a 15 minute walk away that lots of people went to to relax which was fun.
From Taupo we went to the Tongariro national park and decided to do the Tongariro crossing. The crossing had an optional extra to climb Mount Nguaruhoe, the 'Mount Doom' in Lord of the Rings where there wasn't a path to follow but a hands and knees scramble to the top. At nearly every point in the walk there were spectacular views of the surrounding plains and lakes and the 8 hour trek flew by.