That'd been the finale of the War for the City of Peace Campaign. I ran it almost two years ago.
It was the culmination of campaign ideas I'd been putting together for almost ten years. I'd run the campaign three or four times before either time caught up with us of the group just drifted apart. Finally, it ended!
After fighting and defeating Tiamat, engaging dragons above a burning city, fighting their arch-nemesis inside an opera house, discovering the secret of the Monolith, jumping aboard the Leviathan, defeating Lilith yes (the Lilith), the campaign ended with an epic battle where they had to actually defend their arch-nemesis from an even worse opponent from the dim past. Most of the group died.
It was the most intense adventure I'd ever run. It ended like campaigns should end, with a bang, and period of reflection.
You can find special soundtrack list I made for the adventure here:
My novella, Murder on the Hot Flats, is loosely based on the War for the City of Peace Campaign.
I can be purchased on Amazon.