Valley is one of the two original maps for Gold Rush (along with Icarus), first shown in the open alpha weekend. It has an underground mine, very large team bases, and two large organic walls on each side. It is impossible to fall out of the void in this map.
The side quest for Valley involves collecting the emeralds found in the above ground middle and bringing them to a villager. After a time limit, whichever team has collected fewer emeralds has an Iron Golem spawn in the middle and start walking towards their wall. Once it reaches the wall, it will start attacking the gate until it has broken, after which it will attack the Smelter. Unlike normal entities, the Iron Golem takes more damage from pickaxes than swords, so it's a good idea to switch to the miner class to do more damage. The Golem gets 1x stronger each time it spawns (1x, then 2x, then 3x).