After last year's vacation in France was so much fun, my wife and I decided to visit our neighbours in Belgium and the Netherlands this September for a round trip.

Any recommendations on which places to visit?

We plan for ~15 days (splitting the time roughly 60:40 between Belgium and NL).

Currently we have the following palces on our "short list"

Belgium:
- Bruges
- Antwerp
- Brussels
- Ghent
- Leuven
- Grottes de Han

Netherlands:
- Den Haag
- Utrecht
- s'Hertogenbosch
- Leiden
- Kinderdijk
(we will skip Amsterdam as we have been there several times)

Are there some "gems" and/or "must sees" that we should include but do not have on the list yet (or any special recommendations for the places we already have on the list)? Anything we might remove because it would be somewhat redundant? (the current list already seems long for 15 days so for any additions we would consider removing something)

Any other usefuls ideas/websites etc.?

Thanks a lot in advance for hints