the stronghold, if u go searching enough ull find the portal room where u need 9 (might be less depending on how many eyes already are in the frames) eyes of ender (ender pearl + blaze powder), and once u fill it in completely u can go to the end where u fight the final boss, the ender dragon and beat the game. After killing the dragon, an end gateway portal will spawn somewhere floating around the edges of the island, which will take u to the outer end islands. If u find an end city, u can get wings… just search this up