The Upper City is built underground.
To be precise, it is a semi-underground design.
The entire design concept of Avalon is somewhat similar to a survival game Wang Yunxiao heard of before his traversal, where one uses their wits against cunning opponents. It features a towering yet enigmatic building at its core, around which circles of streets are arranged.
The city's radius is approximately three to four kilometers, with the outer layer enclosed by a high concrete wall, about twenty meters tall, half of which is underground, so from the outside it looks about ten meters high.
Normal city construction is usually near a water source, on high and flat terrain, to avoid flooding.
