Seeing no functional difference between the doors aside from the bitter cold of the blue one, you decide to try the red one on a whim. Turning the handle and finding the door to be unlocked, you give it a gentle push and it swings open to reveal a torchlit set of stairs leading downward. Wondering who would use torches in this day and age, you walk forward and peer down the stairs. Spying nothing other than the staircase stretching downward for as far as you can see, you look back into the pit at the three other doors.
Long moments pass as you think on your situation. You don't relish the idea of going even deeper underground, and there is the possibility that one of the other doors leads straight outside. However, there's also the chance that choosing another door could trigger an alarm, bring you face to face with a guard dog, or lead you to an even worse fate that you have no way of anticipating. Figuring that any choice you could make would present a risk, you decide to trust your fate to your original instincts. Anticipating a long trek downward, you take a minute to stretch out your legs and then begin your descent.
Having no way to mark the distance you travel, you try instead to keep a rough tally of how much time it takes you to traverse the corridor. At around what you guess to be the fifty-minute mark, you shift from the vague 'one-Mississippi' mode of tracking time to the more concrete method of counting your steps. This system lasts to the count of four-thousand and thirty-eight before exhaustion begins to eat away at your ability to keep track. Not having any clue how a stairwell could stretch so far under the earth, you begin to irrationally wonder if the tunnel even has an end, or if you'll eventually discover yourself wandering out of a hole in China.
It is only once you have reached the point of wanting to collapse against the wall that you spot the first sign of something other than torchlit steps down the passage. Starting out as a patch of darkness barely visible in the distance, as you move closer it reveals itself to be a circular archway leading to some shadowy location. Eager for any change of scenery, you begin to take the steps three at a time despite your exhausted state. Not even bothering to slow down as you approach the portal, you take the last few steps with a triumphant smile and stumble out of the torchlit stairway and into the dimness beyond.