first book of a trilogy sees an anthropologist, a psychologist, a surveyor and a biologist enter area x, a strange ever shifting geographical are where an event occurred that has quarantined it from the world and set an indefinable border around it that may or may not be incrementally expanding.
the all female team are the 12th expedition, where all previous expeditions have returned deranged, detached, suicidal or afflicted with aggressive cancers we follow the thoughts and perceptions of the biologist as they discover the spiral staircase that leads down into the earth.
our biologist sees this as a tower and as the team enter they are subjected to the bizarre and alien experiences we have come to love from the author. 
i read this book in two sessions, it's quite brilliant, reminiscent of jb ballard and hp lovecraft, the writing is exceptionally beautiful, the story horrific and yet beautiful, can't wait to get straight into the next book in the series.