A quick way to gain inspiration for a setting is to do a Google image search. It's important to use some specific but not too specific keywords. One might get some great exterior shots of Medieval Castles with those keywords but to get some inside shots, which can help inspire encounters and RPing scenes within settings, add the word Interiors or the words Dining Hall or even Dungeon. Setting influences gameplay at the encounter (and not strictly combat encounter) level.
A Game Master needs to think of himself as does the director of a film, looking for the right location and deciding how to shoot that location when the players are on the stage. Of course, the players in this case have much more volition than do actors with a script. A GM also needs to be prepared to pan the view with the choices made by the players. Because of this mandate, a GM will often fall back on a battlemat or other style of overview map that gives a bird's-eye-view of a location. If one is trying to keep players immersed in a game, this strategy can backfire. It pulls back from a scene in a way that takes players out of the location and makes them think in terms of direction of the scene as a whole rather than from the perspective of their character.
Even if a GM is going to pull back in this manner as a way to plunge into combat, he should keep some descriptive elements available that imagine the setting location through the eyes of someone with boots on the ground. Prior to play, or on the fly if the players are moving into areas that have yet to be fleshed out, it will serve the roleplaying aspects of any tabletop RPG if they take the time to think in terms of the five senses, and in particular the five senses of one or more of the player characters in the room. Get the PCs in the scene, keep them in the scene, and then allow the scene to unfold based on player character actions.