Any place with at least 3 base "structures". (these are objects that have a 20m no spawn zone and are generally interactive elements such as fires, beds, work benches, furnaces, and so forth, but not simply walls, roofs, floors, and such). You have to be within 40m of 3 such objects during a raid check, which happens every 46 minutes. (note there are also raids that pure focus the player anywhere in the world, like with the wolf event).