Wilderness Conditions - For all that my players dread the flooded swampy boat trips of the Cold Fens, the jungle is worse.
Edmund Blackadder: "I hear that conditions in your
Duke of Wellington: "Well I'm sorry, but those are my conditions and you'll just have to accept them."
Movement is a huge key. Everyone is mobile, but no one is mobile enough - and "carry it home with minimal difficulty" trumps "just light enough to get it out of the dungeon." On top of that, the PCs need disease-curing ability, poison-curing ability, a good reserve of FP, and a little luck (augmented by skills) to get through.
Exploration Heavy - The Lost City demands you explore. There is a buttload of treasure-less monsters out there, plaguing the jungle and the city ruins. Even the treasure-owning monsters leave it behind when they come out to engage with intruders/potential food. Finding that treasure takes exploration. Exploration takes time - and time is at a premium.
This has come up in game, offline, in email, and on this blog - taking a long time to fight things means less exploration. The players need to choose between combat resolution detail and time to explore - and this place is exploration-driven.
Fighting is less important - Fighting is a means to an end here. In the Cold Fens fighting some monsters was required, and in Felltower fighting some monsters will open up avenues to explore now or later. Here, it's just a time killer even when you must fight them to get things. Time is running out, and you can't get loot without any fighting but every fight saps your ability to exploit loot before the PCs need to leave the area.
Requires specific targets - As my players found out last session, you need actionable intelligence and specific targets. Even then, you might choose poorly and come up blank. The more details you can get, the more places you can cross out on the map as being less-than-certain to have treasure, the better. If you go in expecting to find a way in, find some stuff at random, kill and loot, and go home . . . you will likely fail.
Skill Focused - Getting into and out of the Lost City requires some or all of:
Usually multiple rolls of each, often for everybody, with consequences for failure that can get ugly. After all, it's an isolated city ruins. It's used as a proof of adulthood/proof of innocence of a crime because it's hard to get to. The original ways in and out aren't accessible to the PCs, yet, so even getting out of the dungeon is tough. This is unlike Felltower (you just walk in) or the Cold Fens (two people with Boating was enough, and Navigation was a once-a-trip issue thanks to an easily navigable path (especially on the way home - roughly North was enough to arrive "home.") Non-combat skills can make or break your trip.
Those are what I think are the biggest, most obvious differences between my other locations and the Lost City.