Kroller-Muller Museum, Otterlo

The paintings collection is quite impressive; also some of the sculptures and installations inside and outside the museum building are very worthy - and I was generally surprised by the size of the outdoors area (although it's a fairly large complex in general). The downside is crowds - it's surprisingly crowded, and its facilities are not up to demand: not enough lockers, lines to the toilets and cafes, full bike parking. It's not a major downside (especially if you arrive early), but might have been better.

One of the best collections that most tourist won't venture to see. Actually very easy to get to by train and bus from Amsterdam. Use a All Holland off peak pass available from the NS office at Amsterdam Centraal.