I once went to a concert at the Royal Albert Hall - entitle "The Organ in Might and Madness". The ticket price included a tin whistle.
The RAH was packed because the concert had been well advertised during the Prom season which had only just ended. We had a rehearsal with our whistles at the beginning of the concert and later on had to all play against the organ - in spite of our numbers, the organ still won hands down. The concert was described as "The greatest structural test that the hall has ever been subjected to". The hall survived, but I think everyone was deaf for the next day or so !

For sheer volume of sound in classical music though, I can't think of anything to beat the "Tuba Mirum" from the Berlioz Requiem. Not only do you have an organ you have a huge orchestra, four extra brass ensembles, and (if you do it according to the score) TWELVE sets of kettle-drums. The chorus basses (and usually tenors too) are expected to sing over this wall of sound. Belioz definitely wished to prove that nothing would prevail over "The Last Trumpet". Once during a dress rehearsal for a performance at Guildford Cathedral, I can remember three (rather elderly) lady chorus members fainting, the first time they heard the full accompaniment !