Alternative entrance to Narnia...

...actually (not so secret) Tunnel, re-discovered in the grounds of Larbert House, in march this year. Built in 1800 it apparently would have taken the small farm track that runs south of the loch to the stables under the main drive of the house. That way wealthy visitors to the country seat would not have to encounter staff.
Didn't dare go inside but my friend did and managed to get few pics of inside, unfortunately tunnel is blocked halfway through.
Apologies for quality of picture.