Slovenia-What to see?

It looks like I’ll be in Slovenia this Spring. We’ll be there mainly for the Slovenia-Holland Euro2008 qualifying match, so we will presumably be in Celje. Also, what’s the best guide book? TIA.

I’ve driven through once, without stopping (we were travelling from Zagreb to Venice). It looked beautiful, and my wife and I are probably going to go there next summer, adding it on to our Croatian vacation.

We have some guide books on order, they should be here next week. So far, all I know for sure is Lake Bled. I understand there are some interesting caves in the southern part of the country.