Take the second portal (black).

You step through the black portal. There is a burst of intense darkness and a sensation of falling...

When you open your eyes, you find yourself standing on a balcony overlooking a vast city-scape that stretches as far as the eye can see. It is early evening; the sky is a mixture of pink and purple as the sun appears to be setting slowly. The moon is full tonight, but the other moon is a crescent... wait, another moon? Then you notice that far below your feet, flying cars are navigating the gaps between the skyscrapers and in the distance a spaceship is rising gracefully into the sky. Is this... the future? Are you even on Earth any more?

You find that you are wearing a dinner suit. Checking your pockets, you find a plastic card which looks like the key for an electronic door, another plastic card that looks like you can use it to pay for things, and... a bloodstained knife wrapped in some cloth. Oh no.

You hear a knock on the door to the room behind you. Is this a hotel? Perhaps it's room service?

"Tantalus City Police! Open this door!"

Maybe not.