One original idea
The crossroads thing, you sell your soul to the devil for…what?
Paint a crossroads on the floor of a gallery, make the ‘roads’ about 4m wide, with the crossroads itself in the centre of the room.
Suspend a microphone above the crossroads.
Visitors will stand on the crossroads and tell the microphone what they’d sell their soul for.
Whatever they say into the microphone will be broadcast into the gallery café.
Should be a laugh.