valley and mountain across.mattress top.very uncomformable.i cannot even sleep on mattrss.have to sleep in another bedroom.retailer told me to push down on hump and it wood eliminate mountain and valley.you guest it .it did not work. my wife and i are very displeased with product. we have actually turned the mattress with bottom on top.was no help.i have back problems was hoping . this mattress would help only increased the back problem.even tried blow air into the sides of mattress to lift out humps. nothing