Here is my current sandbox:
https://sites.google.com/site/grreference/home/05-the-black-mountainI started running my campaign in a small area to the south of here and now I have a couple of continents, a few islands, etc. Most of it isn't as detailed as the above but a large part of it is. If you are in Iron Town and you tell me you want to go x number of blocks in y direction, I will know what neighborhood you are in and have some people for you to meet. However, this is all the result of running the same game-world for decades and it started out as pretty much a railroad, with the characters heading up the Old Northwest Road to see what had happened in the Lake Country since it had become isolated from the rest of the nation.
If you are in the Westwood and you head in x direction for y hours, I have an idea of who you might meet.
About that inn that some GMs are willing to move to wherever the PCs wind up and others aren't, I have the inn at the high point of the pass and several inns in Iron Town Above all set but there ought to be one inn between the high point and Iron Town and I am only roughly ready for the player-characters to go into Iron Town Below. But the main thing I wanted to mention is the Inn of Indeterminate Location that I got out of Joel Rosenberg's Guardians of the Flame Series. It's a very nice Dwarf-run inn that has never actually showed up but there's a random chance it will.
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https://www.drivethrurpg.com/product/218159/Glory-Road-Roleplay-Core-Rules