A portal is a (generally) temporary gateway to a special level. Each such level has multiple possibilities for its exact layout and inhabitants, but always follows a specific theme. You will almost certainly encounter some of these in every game, but it is extremely rare to ever find all of them in a single run-through. In the console version of Crawl, portals are represented by the ∩ glyph.
Portals are either silent or announced. Silent portals will exist until you enter them, even if you leave the level. Announced portals are timed, and will eventually close if you do not get to them fast enough.
When a portal times out somewhere out of sight, you may get a message such as: "The floor vibrates strangely!" Treasure troves and Ziggurats won't ever time out, but after they are used once, they may never be entered again.
The following comprises all portal levels, with their in-game description and a brief explanation:
- A sand-covered staircase
- Zombies and mummies and traps, oh my!
- The Sewers
- A glowing drain
- Wade through rat- and snake-infested waters. Mind the kobolds.
- A flagged portal
- Ranged weapons and/or a slugfest with orcs, gnolls, elves, and goblins.
- Ice Cave
- A frozen archway
- Assorted frigid monsters and ice statues abound. Bring cold resistance and watch your potions.
- A labyrinth entrance
- Find the exit, beat the minotaur guarding it. Bring extra food.
- A dark tunnel
- Everything is on fire. Including you and your scrolls, if you forget your fire resistance.
- Wizard Laboratory
- A magic portal
- The private laboratories of any one of several strange characters.
- A gateway to a bazaar
- Shopping trip!
- Malign Gateway
- A portal to somewhere
- Not a true portal, but the short-lived result of a spell: eldritch tentacle imminent. Walk into it to blink and take some damage, if you really want to.
- A portal to a secret trove of treasure
- A collection of treasure customized for your character... at a specific, peculiar price. (No portal timer.)