What is circumambulation? I read about this from time to time-- usually in reference to the stupas in India that held the Buddha's relics.

What was the point of circumambulation? Do any sects of Buddhism still practice this?
Circumambulation (Walking around something clockwise) is still a very common practice in most schools of Buddhism as a form of veneration of something. 

It is done for Stupas containing relics of the Buddha most famously, but also for other things as well. For example, in the Theravada tradition it is common that on certain occasions one would circumambulate the entire temple or monastery, and I think this sometimes done in other traditions as well. 

In Chinese and perhaps Vietnamese Buddhism it is common to circumambulate the main Buddha image of a temple and so temples often have an open path that goes around the image so you can easily do so.