Grosmogesson
A folly, usually Victorian, though any old, old building (i.e. 50 years old or more) could qualify. It must have exactly two distinct major access routes and a staircase around the interior wall to allow visitors to climb onto the roof. The roof must have a waist high wall around the edge, a ledge about eight feet below the roof and afford spectacular views of the surrounding area. The most dangerous feature of the Grosmogesson is the metal dish at the top that has no function except to lure curious travellers to their deaths. The worst thing about this is that the unlucky person does not fall straight to the ground—instead they find themselves trapped on the ledge, leaving their hapless comrades to poke them to the ground with a large stick.
The Colonel's Regiment managed to find a Grosmogesson during their excursion on Mission 6 
6 Heidelberg. Rupert nearly fell for the trap (quite literally), but Mike, David and Steve were alert to the potential hazard and managed to rescue him.