"I recommend Mercat Tours; it's a family-owned company that specializes in touring the vaults beneath the city — a labyrinth of tunnels first used as storage and workshop space in the early 17th century — and it's the only operator offering vault tours during the day. They run adult-only tours that include the infamous Canongate graveyard, and they also offer vault tours designed for kids. Tours start at 20 GBP." - Matthew Kepnes