Each player has one or more characters generated according to standard points buy D&D 3.5 rules with a level appropriate value of equipment. At the start of each session one player is chosen to be the GM-de-jour. They GM that session while their character enjoys a well earnt rest. The rest of the players then choose a portal to explore, which will set the encounter level of the session’s adventure. The GM-de-jour will choose a special condition (eg low light, earth tremors, low ceilings, portal leads to an elemental plane) and a mission, something the council of Hacston want done (eg, kill the dragon, rescue the prince, frame an Orcish tribe for the murder of an Ogre).
Characters enter the dungeon through a portal, and typically find themselves in a dead end corridor. The portal can be used by characters to return to Hacston, operating it to do so takes a full round action which provokes attacks of opportunity. One person can activate it and another can pass through, useful if someone is unconscious. After a person has passed through it, the portal will need to be reactivated for another person to use it.
Additionally each character has an amulet of returning, a magical item usable once per day provided by the council of Hacston. Using it takes a minute, provokes attacks of opportunity and only the person the amulet is attuned to may use it. At the end of the minute that person is teleported to Hacston, outside the portal they entered.
The rooms containing the portals are well equipped with healers. Upon returning to Hacston a character can receive first aid stabilization for free, or any curing, healing spell, poison neutralization or restoration spell for the book price. These will be applied the round after the character needing aid passes through the portal.