My current Arcana Evolved campaign has seen the unnamed and ever-shifting group of Adventurers take up residence in various places. From levels 4-12, they resided in a series of inns, haphazard camps, and at a two-month stretch, aboard a pirate ship called the Ebon Gill. Eventually, they moved into the southern jungles of my campaign setting, where they braved the dangers of the Saahuet Kha, the Asaathi Temple of Changes, and cleaned it out.
Subsequently, they offered up the Temple as a new home for their allies, a cabal of magic users and alchemists, who have offered to co-habitate with the PCs as part of a mutually beneficial arrangement. The Research Colony supplies arcane assistance for the PCs, and in exchange, the PCs offer them protection and occassionally run "errands" for them. This pact has been further expanded to include Zardozan, a former member of the cabal who entered the temple over a decade ago and attempted to use the artifact at it's core to transform himself into a Green Dragon. The attempt was only partially successful, leaving him as a Woodwrack Dragon (Creature Collection I), suffering from a progressive mental degeneration which leaves him with a child-like mentality (6 Wisdom). Zardozan is not trusted by the cabal, and so he works for the PCs, watching over the temple when they're away, offering aerial transport, and the occassional air strike, in hopes that the PCs will use their pull to get him another shot at using the artifact to "fix" him before his condition worsens.
After the Serpent People attempted to re-take the temple with a force of Fifty ECL 10 characters (and were brutally slaughtered by the level 12 party and the dragon), the PCs became involved in the war between the Snake-creatures and the other races of the jungle, which has lead to the addition of a Tribe of Grippli to the temple's residents, adding a dose of shamanistic magic, and a sizable force of stealthy Rogues and Scouts to defend the temple while the PCs are away taking the fight to the Snakes.
Physically, the Temple of Saahuet'Kha is a 4-layered Mayan-esque temple, with a cylindrical chamber forty feet wide straight up through it's center. A pair of twisting ramps line the inside of this cylinder and provide the only means of access between levels. The top of the temple is a raised platform over the pit, surrounded by 5 dragon statues, each one serving as a focus for the primal elements and energies gathered in the lower levels of the temple.
This entire assembly is a single artifact, known as the Evolution Engine. When activated,
arcs of energy leap through the central chamber, creating a double helix between the ramps, and directing the energy upward, where it is focused on the person or thing standing on the platform, which is then torn asunder and rebuilt anew. Under ideal circumstances, this allows the PC to perform various changes to their character, adding Evolved Levels, or rebuilding the character's levels, abilities, etc. as per PHB2.
The operation of this device is a tricky endeavor, as the only instructions are in an ancient dialect of Draconic that even the Loremaster who heads the Research Cabal has difficulty transcribing. Zardozan's condition is a testament to how things can go horribly wrong for the user of the device, as is the incident which occurred the first time a PC used it. No one suspected that the summoned Quall's Feather Token Tree sitting in the central chamber would disrupt the flow of energy through the temple. In the resulting accident, the Negative Energy was focused downward, and into the tree, while the Positive Energy was forced upward, and into the PC Sorceror. When the conflagration ended, the PC (who's player was planning to leave the game that session anyway) transcended his mortal form and became an Thaerestian Arcane Angel (Complete Book of Eldritch Might), while the tree was warped and mutated into an Iron Maw (Fiend Folio), which promptly turned hostile, and had to be destroyed.
Since then, the PCs have successfully used the machine properly twice, but the accident has given many of the Players pause when considering the risks involved. Sometimes having the ability to completely re-define your character right in your own home can be more disconcerting than it is cool.
Soon however, the PCs will probably be moving on...one of them has a claim to her homeland's throne, which, if she is found worthy of it, could give the PCs the ultimate "home base"...and entire country!
Robert "Habitat for Insanity" Ranting