Ground floor

Intended to plant a rose in the back garden today but got down just over a foot and hit something solid. After scraping the soil back I uncovered this. 
Our house was originally built as a Victorian ale house sometime before 1850. It has no cellar as this is fenland and the water table is high. We had been told that there there used to be outhouses at the back which were used for storing the beer so this is probably outhouse floor. When you look at our garden in relation to the surrounding area it is visibly higher so the thought at the moment is that when the outhouses were demolished the area was covered with topsoil. The question is how far does this floor go? Very tempted to uncover it all but it could be a rather large project! Meanwhile the poor rose is waiting to go somewhere else. 
Possibly one for Derelict Sunday? Thank you for hosting DS, Marlieske.