Silo

The silo is an abandoned missile silo buried in the ground. Many of the concrete blocks are damaged or mossy, despite this, the silo still functions fine.

Where to find
It can spawn in any biome.

Dangers
It's not particularly dangerous, but don't explode explosive barrels near you, fall down the silo, or fire a missile at yourself! The bottom of the silo can get pretty dark if you put a hatch ontop and hostile mobs can spawn in, the most dangerous being creepers as they can destroy the redstone wire used to fire a missile.

Loot
There are three loot chests as well as a missile launchpad.

One chest is in the control room. It contains common items.

One chest is right below the control room. It contains missile-related items, sometimes even missiles themselves.

One chest is hidden behind a wall to the left of the control room, on the missile floor. It contains more weapon-related items.

Refurbishing
As stated earlier, the concrete has degraded quite a bit since its abandonment, but the control room can still launch missiles just fine. Use the ladders to climb down, add a battery to the launch pad, a missile, a target designator and you're set. Replace the degraded concrete if you want, but it is still sturdy and blast-resistant already.

If you want to add a hatch, just add some internal lighting and make sure you don't forget to open it before firing a missile!