Yellowstone is the best place to see geysers "half of the worlds geysers are in Yellowstone" 2nd place would be Valley of Geysers, Russia You will find the rest scattered all over from, New Zealand, Iceland, and Chile
There are geysers in Iceland because there is hot, molten rock, called magma, under the ground in many places in that country. This heats the geysers and hot springs and drives the island's many volcanoes.
Geysers are caused by pressure under the earth's serface, kind of like a tea kettle, the magma heats the under waters springs untill it explodes. So geysers are found near hotsprings deep below the serface.