http://www.show.me.uk/ is a wonderful place to start searching for interactive and engaging web resources to support all sorts of topics!
It brings together all the best on the web from the UKs galleries and museums up and down the country.
I use these on my VLE all the time by creating links from static images but, if you are up to the task, there is no reason why you couldn't embed them using an iframe.
As I say these are from museums and galleries in the UK and so all are safe safe, but as with all web resources, make sure you check them through for suitablility first!!!
