Canberra's Answer to Glamis

As a child, I was fascinated by reports of Glamis Castle and its mysterious hidden room. Supposedly, if you were to hang a towel out of every window at Glamis and then go outside and look at the facade, there would always be one windowsill remaining bare. What was behind that window? What ghostly face could be glimpsed peering through the glass?

Little did I know that here in suburban Canberra we have our very own Glamis mystery. Yes, the heritage bus shelter just down the road from us also guards its secrets. At first it appears to be so ordinary, but within it a riddle lurks.

Look, here is the shelter seen from the front (honestly, how did I manage not to get the thing centred - I had hoped that with practice my compositional skills would eventually improve, but no):

Here it is from the back:

And here, (and this is where things get spooky), is it from each side:

Do you see that big bit sticking out at the back? Well, now look inside the shelter:

There is no doorway in there or on the outside leading to that bulging extension. The space is entirely enclosed. What have they walled up within that hidden room behind the benches? Canberra very rarely gets this exciting.