This guide will let you know how to unlock the Lost Settlement Secret Mission in Minecraft Dungeons: Creeping Winter DLC. You have to follow all the steps carefully to unlock it.
To unlock the lone fortress, you will need to travel to the Frosted FJord. It is the first level you can pick when you have the creepy winter DLC in your game.
When you start the level, you have to find the source and pulse. You will need to use the ghost cape, a death cap mushroom and the boost of swiftness, which will make the run a lot faster and easier. You have to be careful with all the pools of ice, and at some point, the gate will hold you, so there you have to survive the ambush, and after that, you will be able to go through the gate as shown in the image below.
You will find a lone fortress secret mission when you go through the gate. You need to follow the objective and activate the pillars. These pillars will activate the gate, leading you to the gates of maria.
There, you have to pass the S shape tunnel. Later in the game, you can also select to follow the objectives or your GPS and go another way. You have to stand on a wooden bridge, go towards the square room, and there you will find some Minecraft tracks with beams of water, as shown in the image below.
You will also find chests in this place, and once you get outside of this cave, you will fight with mobs, and after the fight, you will find another door that will take you back to your objective.