If you're in New Zealand and want to have the coolest playhouse/LARP-prop south of the equator, this Trademe ad is offering a concrete water-tank converted to a castle for a surprisingly reasonable $500 (you have to pay to move it, though).
Castle Playhouse (Thanks, Edwin!)
This one off creation from an old concrete water tank makes a unique playhouse.
Downstairs dungeon with gate.
Ladder leads to timber & ply 1st. floor.
Painted roof to form turrets.
Pictures do not do it justice.