>>40608547
To be fair there's a bit that would seem slightly contrived, had it not been for the DM's disappointment, the sense it makes in story and the fact that it was a stroke of brilliance from the Bard (of all people) that managed to give them a massive helping hand in unfucking the place.
Edinburgh: the capital, very hilly, towers for rituals, massive castle, inhabited for centuries, even got roman remains, surrounded by necromantic wastes that resemble an area that's been nuked, swarming with undead and necromancers. All the necromancers save the BBEG, who they have a beef with are in a ritual, but he's a tough bastard.
That castle has is one of the most besieged places in the world, it's tough as hell (though the wizard got them up the cliff), and is quite rightly being used as a base by the BBEG
It's also home to a big cannon in the castle's main battery, generally used for signalling one o'clock, which they then used to kill all the in-ritual necromancers, and the BBEG's recombination of defeated skeletons.
Like I said, if it hadn't been for all the sensible factors and the unlikelihood of the bard suggesting it (the DM could probably have said it wasn't there, but it's a famous feature of the castle that's pretty unique, so that would have been a dick move) it'd seem like a really lame cliché, the villain leaving such a convenient tool to defeat the wider plot.
As it was, badass