A. J. Berrick has an interesting paper explaining how a topologist thinks about group theory. Topology and group theory are connected throught the fundamental group. For every group, topologists can construct a space with that group as its fundamental group. Some of these can be very complicated, even for comparatively uncomplicated groups. For example, perfect groups lead to very scary-looking constructions.

The paper is A topologist’s view of perfect and acyclic groups.