I can't find iron clad proof, but a poster on reddit claims that Bruce's stack of pianos was placed there by the Danny Hughes Beat It Music shop in Blackrock, Louth, Ireland as part of a charity event supporting Cross Cause charity. There's apparently a tall post behind the pianos holding them all straight. I did find
another picture at the same location where a tall pole in the same spot had been outfitted with a viking sail during a film festival, and there's more stuff on the internet of artsy burning man style events located at the same place.
Edit:
Conor Hughes is behind it, and
here he is, perched on top of the pianos.
Edit again: I found a newspaper article teasing about his then upcoming piano stunt.
https://www.independent.ie/regionals...-36418130.html