You mean the woodland mansion? They were added a few versions ago, usually you have to buy a map from a cartographer in a village to find one. Finding one randomly like that is pretty rare, you lucked out. They have a lot of new mobs in them, that can be pretty tough and kill you easily, look it up on the wiki.
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To tell them how to live is to prevent them living.
That's a woodland mansion, a new sort of "dungeon" that was introduced in an earlier update. It is guarded by sort of evil villager (illagers), one variant of which is a vindicator who is equipped with an iron axe(he hits hard, watch out!), and then there are sort of illager magicials, they summon a bunch of things towards you and are the only mob who drop the new "totem of undying" which is basically a revive when you hold it while dying. The mansion itself is quite huge for a minecraft structure, and you can find some pretty good loot in there (though it's not as good as the loot you find in end cities)
"A woodland mansion is a very rare structure found only in the roofed forest biome. It is the only place where the vindicator and evoker mobs naturally spawn. Woodland mansions generate very rarely in roofed forest biomes, often appearing tens of thousands of blocks away from the spawn."
They've been in the game for 9 months now, but they're very rare and very hard to find without commands or a cartographer's map.
Don't even think about going in unless you have full diamond enchanted gear. Those Vindicators are pretty tough and will kill you dead in two hits without armour. But if you manage to kill an Evoker they drop something pretty neat, which I won't spoil.