Everything takes place in a "scene". Whether it is the "Climactic encounter in the Cultist's Lair", or the "Hallway encounter with a shambling mound." The points that connect them aren't important enough to spend much time in.
Just as you wouldn't map out and take time to deal with each step the party takes while travelling from the neighbourhood tavern to the mage college, you don't need to do this in a dungeon.
You may say that this takes away player choice; don't players have the right to choose which dark, dank passageway they want to head down? This may be true, if you're playing an entirely tactical game, where every choice may be important. Lots of people play this way, and it's a fun way to play the game. But others don't want to have to detail each 30' long corridor or dead-end or empty room. You want to get to the meat of the adventure.
So what you do is come up with a flowchart. To get to place X, they have to either take path Y, leading them through places a, b, and c; or take Path Z, leading them through places d, e, and f. You still get all the excitement of the dungeon, but you don't have to wander around doing nothing for a while.
I started using this method while playing Star Wars. There was no way I was going to be able to "map out" and entire Star Destroyer; so I let the players tell me where they wanted to go. "We'll try and find the power core, you guys head to the brig, and you guys try to reach the docking bay." Each group might have an encounter that impedes thier progress, but exactly where in the ship that happens, or exactly where in the ship the brig/power core/docking bay is, isn't important. What happens to them along the way is.
It's like a movie - you don't have to see the whole journey, just the important things that happen along the way.