Day 6 - How can players make a world seem real?
Good question, and not an easy one to answer.
I think that part of this comes down to the GM, especially how they present the game world to the players, how descriptive they are about the world with their players. Description doesn't just stop at geography, however, it also should incorporate cultures, little things like habits of inhabitants in an area the characters are travelling through, what kinds of rations I can buy in the small town at the edge of the mountains, and so forth. Frames of reference are good for this player immersion, and giving the players something that connects them with the world (be it a person, a structure, a location, etc.) starts the process nicely.
However, players also have some responsibility here. First of all, buying into the game world itself is a step in the right direction for players, and if the game world gives them that sensa wonda feeling, then all the better. Another way of players making the world seem real is having players contributing to the game world. This can be as simple as inserting some minor location or area into the game as the players are playing the game or can encompass much more, perhaps where a player designs a country for adventuring that the GM inserts into the game world.
When it comes down to it, player immersion into the world is a key to this.