Minecraft Dungeons:Church

The Church is a building accessible after the hero completes for the first time. It is reachable via a path to the left of where the hero finds the broken nether portal. Once the hero reaches the Church for the first time, a drawbridge is able to be lowered to make reaching the Church easier. The Church allows the hero to unlock the runes, allowing access to the secret mission and two Obsidian Chests.

Inside the church are several developer portraits found in the credits for the game. In the end, there is a dog portrait. Clicking on the dog reveals a hint towards the location of an undiscovered rune.

Unlocking ???
Upon completion of Obsidian Pinnacle, and then activating the button in the back of the church, several secret areas appear where nine must be collected. A painting inside the church gives hints on how to unlock them.

NOTE: The levers/buttons that open the rooms containing runes generate only after visiting the church, which requires defeating the Arch-Illager on default mode.

After the hero collects the nine runes and returns to the church, the golden button with a cow face unlocks a room with two obsidian chests and a map, which reveals the secret mission. On the level selection map, this can be found behind the in the northwest corner of the map.

Trivia

 * The runes required to unlock the Mooshroom Island spell out the words "BOVINE PATH", as can be seen in datamined files.