What an interesting photo!
As a youth I grew up in Southeastern Iowa and the cemetery where this is located is in Burlington, Iowa.
Aspen Grove was recently contacted by an aquaintance of mine and they told her this was used as a "Receiving Vault" back in the 1900's. It was built in 1933. This is where they stored the bodies until they were ready for burial. This vault has been closed now she said at least 60 or 70 years. Nothing is stored in there because they can't hardly get the doors open.