The Sky Lounge is a café and restaurant on the top (11th) floor of the Double Tree Hotel, near the Central Station.
It is particularly well-known for its nice views, overlooking the old town of Amsterdam on one side, the IJ and Central Station on the other side.
There is also a roof terrace.

Food and drinks are not cheap here (but WiFi is free).

Address:
Oosterdoksstraat 4, Amsterdam
Web:
http://doubletree3.hilton.com/en/hotels/netherlands/doubletree-by-hilton-hotel-amsterdam-centraal-station-AMSCSDI/dining/skylounge.html

Opening hours:
Su-Th 11am-1am, Fr-Sa 11am-3am