The council said it could make compulsory purchase orders for dangerous buildings, in extreme cases.

BBC: Former Eagle Mills Dundee

"Because of the property crash we've discovered the number of derelict sites and dangerous buildings has increased enormously, " said Mr Martin.

BBC: Ratepayers' ?300k bill to clean up development site

Often, though, their lack of capital means they are unable to teach a broad curriculum, are short of books and other materials, and are stuck in unsuitable (or even dangerous) buildings.

ECONOMIST: Private education

John McCormack, who owns several nearby properties and is an expert on historical buildings, said knocking down older buildings set a dangerous precedent.

BBC: Coupee Lane site

There have been at least 710 aftershocks, further damaging buildings and leaving them dangerous.

BBC: China quake kills scores in rural Sichuan

Sewers can contain dangerous gases, subway systems can have unpredictable train schedules, abandoned buildings can be crumbling or have asbestos, and usually it is illegal to access the sites.

BBC: Discovering an unseen urban underworld

As is well known to participants in the sport of Base Jumping (a mind-bogglingly dangerous activity that involves parachuting from static objects), parachutes have problems when launched from tall buildings.

ECONOMIST: Safety