There are several types of rooms that you may encounter that have special designations. These can include Arcades, Shops, Arenas, and Treasure Rooms.
An arcade has several diversions for players to have a chance to get more money, or other items, if the are lucky. These rooms are marked by a special door displaying arcade on the top, and it costs 1penny to enter the room. Inside of the room itself there is a Blood Converter, a Skulls Game, and a Slot Machine.
Isaac can play the game for 1 penny, which is based on the old shells game. The player pays by walking into the minigame, and a prize will be hidden under one of the 3 skulls after a quick shuffling routine. If the player guesses correctly, they will receive more money, a key, a powerup or a heart, and if they fail, a single fly will be released, which will attack the player. On occasion can give player skatole, and will vanish when this occurs.
Care should be taken if you do not want to play the game, as all you have to do is walk into the game to begin play.
If the player is doing well on health, they can conver their spare hearts into pennies at the blood converter. 1 heart will earn the player a penny, which is generally not worth the price, unless you need the extra money to buy something from a store. May explode, giving player, blood bag.
The player can play the slot machine to try winning a key, bomb, money, pills or hearts, each spin costs 1 penny a play. If you lose there is a chance of releasing an enemy, as opposed to the guaranteed spawning of an enemy with the Skulls Game. The downside there is a lesser chance of winning the game with a desired outcome, as there are more prizes. If used repeatedly the slot machine can explode, giving out a reasonable amount of money (around 5 coins) and some hearts.
Shops are encountered regularly in the game by the player as they explore levels. In each the player can buy items for the money they have collected in the game, and they are run by a shopkeeper, who is a baby hung from the ceiling. Items are bought as soon as they are walked into, provided the player has enough money to afford it. There is a slight chance of having to fight Greed on entering a shop instead of entering the shop as normal.
Arenas are marked with a grey door with crossed swords on them. You can enter there onlly with full hp. On entering a room you are given an item, and then enemies will spawn in three waves. After killing all the enemies in all 3 waves, you are given another item, and the door will unlock, allowing you to leave the arena.