The whole clue is a cryptic definition. On the surface, "pants" suggests underwear directly, but the real cleverness is in the word "Like" — Bishop Auckland is a town in County Durham that sits on the banks of the River Wear, so it is literally UNDER WEAR (under the Wear). Like Bishop Auckland's pants? works because the town could be described as "under Wear" and "pants" is a synonym for UNDERWEAR. The word "pants" also tempts you into thinking it's an anagram indicator for AUCKLAND'S, which is a lovely misdirection.