All tickets for a free theatre and art show in disused railway arches at Waterloo Station have been snapped up in less than 24 hours.
Now all has been revealed. Hundreds of free tickets have been snapped up via the mysterious website at www.tunnel-228.com
Visitors enter via a small door on Station Approach and exit into the middle of the Leake Street tunnel.
Writing on Twitter, Kevin Spacey said: "Never expected Tunnel 228 to sell out so fast. Opened last nite & was awesome."
He also confirmed plans to bring back the show in the autumn for an extended run.
Since then the profile of this previously forgotten street, blocked off to traffic when Eurostar left Waterloo, has risen considerably.
Earlier this year speakers playing piped classical music were installed in the tunnel.
Meanwhile SE1's other experimental subterranean theatre specialists, London Bridge-based Shunt, have announced details their new show Money to be staged in the former cigar warehouse in Bermondsey Street.
On Thursday night Bermondsey Community Council was due to consider Shunt's planning application to turn the disused warehouse into a temporary theatre.