As the title suggests, this photo is of a small drydock at Cape Town harbour. For those who perhaps don't know, a drydock is used to perform ship repairs that cannot be done while the ship is in the water.

Essentially what happens is that the vessel enters the drydock (which is still filled with water). The wet drydock's gates are closed and after securing the vessel, huge pumps pump every little bit of water from the huge swimming-pool-like container. I'm guessing that the process is carried out fairly carefully, as one would have to ensure that the vessels are properly supported as the water is drained. Imagine having one of these topple over in the dock...