Amsterdam's Rijksmuseum. The Night Watch is there.
Just a little note there. The Rijksmuseum is undergoing massive renovation. They moved the most important pieces to a small wing. Currently, you can ONLY visit that small wing. You'll have to wait a couple of years before you can enjoy the Rijksmuseum in its full glory again.
And another tip for Amsterdam. Amsterdammers tend to speak English reasonably. Being bi- or trilingual in Amsterdam is considered normal. So asking a local wether he or she speaks English is considered somewhat rude!
To conclude, here are some more tips from an Amsterdam native!
- Have coffee at the La Place restaurant of the Public Library (Openbare Bibliotheek) near Central Station. The view from the terrace on the 7th floor is amazing! And from the library you can easily walk to the Amsterdam, a replica of a 17th century Dutch United East India Company ship.
- Have lunch, or another coffee, at the Blue cafe at the Kalvertoren. It's basically a cafe build into some sort of glass tower giving you an awesome view of Amsterdam's 'skyline'.
- Amsterdam's red light district is somewhat of a tourist trap, although it does get mildly dangerous after midnight. The walking tours given by the Prostitution Information Center are great though and really informing.
- Try to avoid taxi's. They're crooks. Public transport is very decent in Amsterdam, though not that cheap compared to other cities.
Have fun!