The Charles bridge has towers on both its end points. There are two towers on the end point that leads to Mala Strana or Little Quarter. There is a gate between the towers.
The towers were built at different times. The smaller tower was built in XII century basing on the Roman tower. This was forming the fortress of the old Judith Bridge (Juditin most). The higher tower was built later in 1464.
At present you may rise to the top of the tower to have nice view.
This photo is the photo of the Towers of Mala Strana made from the Charles bridge. The image was shot using Canon EF-S 18-135mm f/3.5-5.6 IS lens @ 30mm @ 10 sec. Also, another image was fused with this one (made with another exposure time to replace very highlighted areas).