What lies behind?

I have absolutely no idea what lies behind this door. It's set in the wall of Frome's 'Via Crucis', a processional entrance route to St John's Church. I've never seen the door open, never even seen the gateway that leads to the Via Crucis open, and not being a church-goer, wouldn't know who to ask.

The Frome 'Via Crucis' is a sequence of just seven sculptured scenes in contrast to the more commonly found fourteen scenes depicted in 'Stations of the Cross'.

Thank you for all the comments and stars for yesterday's Tryptych - it seems that I wasn't alone in finding the artwork rather beautiful.