london is a higgledepiggldy place. it's not uncommon to find two building next to each other with a random overhead tunnel connecting them. often these walkways are angled up or down to reflect the different levels of floor heights in the adjacent building.

but what if one building is built at 90 degrees to another ? what if one building has gravity working downwards, but the one next to it has gravity working sideways ?

well, the answer is to have an overhead tunnel with a rotation slightly built in.

if you come to london you really should track this amazing gravitational altering device out. It's in Covernt Garden next to some theatre.