So here's something big that I'm playing around with....
In Profundis gives you a limited inventory for carrying around equipment. You tend to use up resources while you're exploring the game world, placing pitons, hanging ropes, and so on. Eventually you have to travel back to base and resupply.
A concern that I have for the game is that this travel back and forth, between base and the frontier of exploration, could get annoying, or worse, boring. But the resource and time costs of getting around the game world are the primary obstacle to exploration. How do I reconcile the two?
My idea is a special inventory item: flags.
After you explore for a while and figure it's time to return to base to resupply/get some rest/buy new stuff, what you can do is plant a flag at a place you'd like to return to later.
After this is done, the challenge is this: return to base without using any other items in your inventory, in order to "establish" the flag. It's like a mini-game in a way. It is okay to use items you've already placed, so you can sort of pave the way for your return trip. If you're forced to use an inventory item the only thing lost is the establishment run. In that case the flag remains where it is, and you can try it again just by returning to it.
The reason this has to be done is because the game is recording how long it takes the player to do it, in order to figure out a realistic travel time, and using resources along the way that might not be available later would spoil the experiment. (It's possible that this might just be "shallow travel" equipment, like jetpacks, rather than things that change the game world to make it easier to traverse, like pitons and spanners.)
After you've established the route, you can later "instantly" warp between base and the flag. Instantly is in quotes because this is only immediate to the player -- the game clock is set ahead by the amount of time it took to make the trip. Since the expedition is charged rocketship rental by the amount of time spent on the planet, this is a substantive cost, but it's your character who has to pay it, not you. The character is still making the trip, in effect, on autopilot. (In fact, I'd like there to be a "montage" of still shots of the trip, that takes a few seconds to play out, whenever warping.)
Continuity of the game world is very important I think. The problem with teleporters is that they basically make a mockery of the spatial extent of the world. I consider this bad because, as the player makes longer and longer expeditions, the increasing time required to get from base to the exploration frontier is, itself, an increase in difficulty. Exploring the other side of the map takes more time, which incurs more spaceship rental costs, which means the player can't afford to waste as much time.
Some of you are no doubt reading this and thinking something along the lines of: WTF? I think I can understand that. But I look at it this way: I've played hundreds, if not thousands, of video and computer games, and I've never known a game to do something like this. Maybe there's a reason for that. But it's a very interesting game mechanic to think about, and I think that will transfer to play. What do you think?