The Hollow Places - T. Kingfisher

Recently divorced and staring down the barrel of moving back in with her parents, Carrot really needs a break. And a place to live. So when her Uncle Earl, owner of the eclectic Wonder Museum, asks her to stay with him in exchange for cataloguing the exhibits, of course she says yes. The Wonder Museum is packed with taxidermy, shrunken heads, and an assortment of Mystery Junk. For Carrot, it's not creepy at all: she grew up with it. What's creepy is the hole that's been knocked in one of the museum walls, and the corridor behind it. There's just no space for a corridor in the museum's thin walls - or the concrete bunker at the end of it, or the strange islands beyond the bunker's doors, or the whispering, unseen things lurking in the willow trees. Carrot has stumbled into a strange and horrifying world, and They are watching her. Strewn among the islands are the remains of Their meals - and Their experiments. And even if she manages to make it back home again, she can't stop calling Them after her...