couple of videos of 'shibboleth' at tate modern:
it's behaviourally interesting as much as anything, as so often with turbine hall installations. the insides of the crack look too fake for my liking, but it's amusing enough. you could lose a phone down there - presumably they have a way of cleaning stuff out, or maybe not - time will tell. adam suggested scattering LED toys that would twinkle in the depths. how about flyers? love notes? prayers? use the crack as a labyrinth path?