It's an iron golem which I created, and a computer-generated building. This golem was created outside the garden and had been happily wandering the village for days. The village isn't large enough to spawn its own golems. The inn and garden are unaltered. I have seen no sign of endermen placing blocks next to the inn, for the golem to climb onto and fall in.

So how on earth did he get in there??

They're too tall to go through doorways (aren't they?) - and this one would have had to have gone through /two/ doorways to get where he is now - and they can't open doors for themselves, which means villagers would have had to have opened both doors for him - wildly improbable. So I assume this is a clipping problem. Are there any other possible explanations?