A Secret Room Was Not Mentioned In The Listing

While cleaning out the basement, Jerry noticed a large piece of plywood leaning up against the cinder block wall. Definitely out of place, he pried it off. Apparently the wood was hiding another room because Jerry discovered a gigantic hole in the wall where more cinder blocks should be.
As a new homeowner, finding a secret room that the real estate agent was unaware of was cause for a little bit of concern. What was inside?