Dungeons are part of the world gen process, and reserve 1-4 nodes per chunk. They are each spawned in one 25x25 area of the parent chunk, so they are a bit spread out.
Dungeons are composed of a few important parts: rewards, max explorers, difficulty, and accessibility. Each dungeon has rewards that rotate weekly, and are randomly chosen from a list of: stone, clay, wood, and keys. When a dungeon rotates rewards, it also rotates the number of explorers that can go in. This number will range from 4 to 40, with a tendency towards lower numbers.
When exploring a dungeon, a player can commit resources to do so. They can either explore solo, or request guild help (if they're in a guild). Rewards scale to the number of explorers, so they can explore solo and get into the action immediately, or get guild help for it. Any number of players can explore a dungeon at a time, it's a PvE element.
In addition to committing CryptoBlades heroes for exploration, players may commit armies from their villages. These armies will bolster power when exploring the dungeons, similar to when attacking happens.
Dungeon difficulty is randomly generated at reset as well. Difficulty will be a number from 1-3 and a power level and an element, following CBK combat rules. The number 1-3 is the number of segments in the dungeon (very short, short, normal).
Some dungeons are locked, and require a key to get in. At most, this would be one dungeon per chunk, with keys obtainable from any dungeon that drops them (keys are not locked to a dungeon). Locked dungeons offer an additional reward that is slightly higher than the other 1-2 rewards. Additionally, locked dungeons are always considered to be "long" (4 stages).