A new concept for me. To an avid reader of John Dickson Carr mysteries, this sounds like fun.
This is HintHunt, an interactive locked room mystery game, hidden in plain sight just down the road from Euston Station...Three other London-based "escape games" are listed at the link.
Everyone seems a little wary, but confident, as the girl runs through the rules of the game, telling us that we will get hints from her whenever she thinks we need them (“No one has ever done it without hints, there is no shame in getting hints”), and that each key or code we find will only work on one door or safe. It all sounds rather straightforward and, dare I say, eminently doable – until she drops the bomb that only 50 per cent of people make it out in time.
The next hour passes in an incomprehensible blur of searching, re-searching, punching numbers into safes, punching other numbers into safes, locks, keys, map coordinates and, at one point, a UV torch... The hints that appear on the count-down screen started as a slow trickle, but by 50 minutes in are coming thick and fast.
Addendum: In March 2015 The Guardian posted a feature story on this topic.