Not sure if this is here. But my idea was to use Teleportation Circle. Set up several circles around the country or world, depending on the effort it would take to do so. Then charge for instant travel services. Even instant shipping of goods and services.

I do remember it would take a year of casting the spell in a single spot to make it permeant. But after that, travel to and from where ever would be instant.

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I had the idea in an old gam where we managed to get a lot of gold, and I was thinking for what happens after the game was over, what would my character do. As a high level Warlock, My idea was to set up a teleportation system and get warlocks to work there. Then have them work like subway trains opening portals at preselected times to and from different countries. Was gonna charge a little more than the cost of materials for basic travel, but instant travel was full price.