A hole in an old Roman wall at the end of Crap Alley. It's called Crap Alley because several houses along the south side of High Street are perched over it and anyone passing along the alley are in danger of sewage barrage.
Via the Chapel of St. Oswald in the Assassin's Guildhall. Not that anyone knows where the Assassin's Guildhall is.
Beyond a triple-barred ironbound door in the cellar of the Wild Boar Tavern. Old Bert, the proprietor, is said to allow usage of this doorway for a couple gold a head.
Through the torture chamber under Winton Castle. This is one of the many rumored ways Empress Matilda escaped the siege of 1141. Ask around, every gabber in the city has their own pet theory.
Under a hatch on the grounds of the Cathedral of St. Swithun. The Cathedral is relatively new, the old cathedral was demolished to make way for it. Rumor has it that the entrance to the catacombs are not encompassed by the new floorplan.
Down an ancient well, said to be in a small courtyard between a tavern and a blacksmithy.