Anya suggests that Crow built the city (it is unknown how), and it would have taken years to do so (supported by the very Victorian architecture and machinery). It is also unknown how Crow knew that the Time Crystals were under the island, but since Anya was able to detect residue given off by the crystals in 2401, there is little reason why Crow couldn't as well.
As Cortez and R-110 traverse the many hidden passages of this base, they uncover many ingenious structures such as 4 coal-fired turbines which would undoubtedly supply the community with ample power, as would the waterfall at the end of the aptly named "Easy Street", which we can assume would also be connected to a power generator. Much of the infrastructure appears to be maintained by a gas and valves network which controls doors, access tunnels, rotating rooms and even a massive driller/elevator in the middle of the complex which allows Cortez to bore down into the heart of Crow's operations below.
It seems that, while many of Khallos' Russian troops went down there to work, not all of them did. Based on various minion conversations overheard, it can be supposed that some of them had friends, family, or fellow comrades whom they left behind to go back in time with the Brotherhood to work in Kronia. Two henchwomen discuss the joining/transition process from simply being henchmen under Khallos to becoming a part of the Brotherhood of Ultra Science; a drunk welder in Kronia notes that he misses his girl; a drunk henchman stationed on Khallos' train says that all his friends have left through a "big round wobbler" which took them to a different period in time.
- Kronia's name is probably based off of "Crow".