I've read Matter. It concerns a Culture Special Circumstances operative who returns to her homeworld (not a part of the Culture) to deal with some family business. Her homeworld is a strange low-tech, hollow, Shellworld, with a number of different levels beneath the surface. Some of it's inhabitants don't realise this, and there is a power struggle between the two that do, and a race to uncover an ancient artefact. Many people find it more fantasy than scifi and don't like it for that reason. It is a Culture Novel, but there are no Minds in it, and only one drone that follows her on her journey back home.