Geometry

Went to the Marble Arch Mound, were able to get in without having pre-booked (previously it sounded like you had to book in advance).  It's not that bad.  The worst aspect is the walk up and down the stairs if you have vertigo; the whole thing's just a huge amount of scaffolding with a living wall on the outside.
The best part is the exhibition in the ground floor, of some clever infinity mirrors. This is a detail of one of them