They've been building this subway for years now. Due to the amount of canals Amsterdam has, water tends to get into the soil and soften it. Building a tunnel underground (underneath a river) has been a huge construction challenge and even though a lot of surveying has been done - it can be halted at any time. Amazingly, even with all this construction the city seems to manage as if nothing out of the ordinary was going on. The trams are so efficient that I sometimes question if they really need a subway.
Check out the graffiti just underneath the yellow construction crane. It somewhat looks like a face which has always made me chuckle. This will be the last photograph from 2007 for awhile as I've bombarded this blog with images of that trip in the past week.