Espai Cràter is the right museum for Olot: a contemporary interpretation centre devoted to volcanoes, built in a town shaped by them. It explains the Garrotxa volcanic zone with models, audiovisual material, and enough science to make the surrounding cones more than pretty hills.
Visit before walking up Montsacopa or heading into the broader volcanic park. The centre gives useful context on eruptions, lava flows, and how people have lived in this landscape, which makes the outdoor sights easier to read.