But I'm thinking of something a bit more Russian/Slavic here like a mix of B2 Keep on the Borderlands by Gary Gygax & perhaps B5 Horror on the Hill by Douglas Niles. But what I'd like to do is set this on the alternative Earth that I've been setting my games in for the last couple of months. We got a mix of anarchism Nineteen century & Middle Ages technologies, personalities,etc. But there are parts of Eastern Europe where the Sun hardly shines & knights still roam the countryside. In the Codex Slavorum we finally get the mix of the Slavic myths & the spiritual realms with D&D style elements even though its through the filter of Castles & Crusades. B5 Horror on the Hill by Douglas Niles has a lot to offer in this direction.
As reviewer Danyel W says; "I first read "Horror on the Hill" almost two decades ago, so this was mostly a nostalgia buy for me. Nonetheless, B5 offers much for a modern gamer: a 'sandbox' module that includes both a wilderness with a number of encounter-locations and a well-mapped, multi-level dungeon, and both are populated with interesting and varied groups of opposition. There's just enough set-up to orient the GM without locking them into a specific campaign-setting, so the whole area can be dropped into a campaign (be it a published setting or homebrew) with a few names changed to fit. The primary obstacles to just playing this module 'out of the box' in any modern version of the D&D or Pathfinder game lie in the old, 'Basic' style stat-blocks, the lack of 'balancing' mechanisms like Challenge Rating, and the relatively generous approach to treasure inherent to the older form of the game. As written, some of the encounters (and hoards) aren't level-appropriate for a modern-style four-PC party of fifth-level, much less PCs just starting their careers! Nonetheless, if the GM can spare the time for the necessary conversion work with resources like the PRD, and is willing to either re-balance everything or accept that parties adventuring at the Hill are going to get either incredibly rich or unbelievably dead, "B5: Horror on the Hill" can make for several sessions' worth of lively and entertaining play." Now there are several very important points in this review that come across in this review, the DYI friendly nature of B5, its access ability as an adventure module, & its flexibility as a sandbox adventure.
Douglas Niles twists many of the usual classic TSR module conventions to give us a module that works for both the players & the dungeon master. Ian M wrote on Drivethruprg; "There are four "bad" modules in the B series (in my opinion), and B5 is one of them. These are the ones that feel thrown-together, and populated by random dice roll. The actual journey part isn't too bad, but somewhat contrived. The main dungeon itself is horrible.
However, a little seasoning to taste can resolve all of this to make for a fun adventure. You can time-limit it to push players along, which adds to the module's intensity. It needs this because, if played as a "normal" adventure module, it's pretty dull." The fact that I agree with the 'if played straight its pretty dull" is a fair statement but given n adventure Gothic & Universal horror film filter then things begin to get much more interesting. That's where I'd grab my copy of Castles & Crusades Codex Classicum to add into the mix. Why?! Well the Codex Classicum adds in Greek and Roman sorcery and magic including necromancy and prophecy. Even the most casual reader of the classic myths should know how important Oracles are to the tales.
These elements are seldom used today to set up things in a campaign. This is something I'd love to add in my on going campaigns. I'm still working out some of the details in how I'd love this to all to roll together into a coherent campaign. But I'll keep you readers abreast of ideas & elements as the weeks roll on.