Complex sentence: Below a certain (unspecified) age all Wombles are nameless; upon coming of age, a Womble chooses his or her name by looking through Great Uncle Bulgaria's large atlas until they find a name that suits them.
Split into simpler sentences: Below a certain (unspecified) age all Wombles are nameless. Upon coming of age, a Womble chooses his or her name by looking through Great Uncle Bulgaria's large atlas until they find a name that suits them.