You can see maps and pictures that were drawn when the spanish first arrived on the islands. And paintings of how they think the guanches lived and looked like. You can also see small scale models of the guanche buildings and villages.
There is an impressive collection of skeletons and craniums, and even mumies that the guanches made. You can still see the hair and nails on the mumies.
The museum is not so big, and it's located in the Vegueta district where there are plenty of old buildings and other museums. You can easily check out this museum and many of the other things around here in one day.

