94.7's The Fugitive - and the answer is...

It's either the London Eye or Madam Tassaud's. If Madam Tassaud's has capacity for 400 people (or 400 waxworks) then that's the one. It could be the London Eye too based on the clue's emphasis (staring) and what do you stare with? The London Eye probably does have capacity for 400. They will have to ask everyone who gets off...