Hello there, this is your Minecraft realtor back again! I hope you enjoyed the Ocean Monument base guide, but it's time to pack up, because I've got quite the treat for you- an Ancient City. Spooooky!
Again, the tips and recommendations I have are for Peaceful mode, and on Bedrock at that. YMMV, and especially when it comes to ancient cities.
I would recommend reading through this guide fully before enacting this strategy, as this isn't for everyone. Ancient City clearing is a lot of work, but has some pretty respectable benefits.
Part 1: Finding the damn thing
It should come as no surprise that it's gonna be decently hard to find the ruins of an ancient civilization, but they actually do generate pretty abundantly, and can easily be found if you know where and how to look for them, though we have an alternate option before you begin exploring. Some players consider this option cheating, as it can take a lot of the fun in exploration out of the search. If you value this more, then just skip the Chunkbase section.
Chunkbase
Chunkbase has an online application you can use to search for ancient cities, as well as just about any other structure in the game. They do say that it may not be 100% accurate, but so far it hasn't missed for me. Do be warned that if your world was created before a worldgen change, the chunks you have loaded in may be different from what chunkbase tells you. Just keep searching, and you'll eventually find new generation.
1. Do /seed in the chat. If you're on a server, this may not work. Good. Don't use this on servers. Just look for your own damn self.
2. If you're on Bedrock, this might not have worked. This is because you don't have cheats enabled on your world. Don't worry; go into your world settings, then hit the advanced tab. There should be a button to copy the seed, or you can just write it down yourself.
3. Paste the seed into chunkbase, and switch the Edition and version to the one you're currently playing on.
4. Simply look for the blue lanterns. I would reccommend also toggling everything else off from the bar of icons at the top if you don't want to have everything else spoiled for you.
5. Click the blue lantern to get the coordinates. Chunkbase will only give you the X and Z coordinates; use F3 on java or toggle "show coordinates" in the world settings on Bedrock, and make your first and last numbers match the X and Z coordinates shown.
6. Ancient cities are always located on Y -51, so make your middle number match that. Preferably don't dig straight down, and for the love of GOD make sure you have a path back up.
1. Get yourself a spyglass if you can, and turn your render distance up as high as you can bear.
2. Look for snow-capped mountains. Ancient cities usually spawn under these.
3. Go into caves near these mountains. Make sure you know the way out, but go deeper and deeper. When you start to see sculk, you've hit a section of the Deep Dark. (If you don't know what sculk is, it's a bluish-black, almost starlike formation on the walls, floor, and likely the ceiling of the cave you're in.
4. Place a bed and a chest down, and set your spawn. If you don't know where your other base is, then don't be afraid to leave and come back once you've memorized or written down its coordinates.
5. Put everything but torches in the chest. You'll probably lose experience, but it's better than losing everything.
6. Just explore. Look around the deep dark and try to find a large chamber with lit up areas scattered about. Make sure to sneak. There is a creature called the Warden here. If you set off a shrieker (the alligator looking things) by making noise near it, you'll get what the community calls a "strike". Get three strikes, and the Warden will climb out of the ground, and chase your ass for a pretty long while. You can try and hide by sneaking, but this guide isn't really about avoiding the Warden. Just be on the lookout for both Shriekers and Sculk Sensors (these are blue things with a bit of deco at the top. They pass on any sound they hear, and can set off a shrieker!)
7. If you still can't find the city, check your coordinates. You should preferably be at Y = -51, though a few blocks above that will probably be fine. If you're desperate enough, start strip mining through the sculk in all directions. If you haven't found anything after a while, try a different cave system, or a different mountain entirely. Sometimes they will spawn outside of the mountain's barriers, but they're almost always near a mountain.
Part 2: Clearing it out
I'll be honest with you, I'm BY NO MEANS an expert on clearing out ancient cities, but just remember to crouch and break any shriekers you see. If possible, just go into Peaceful mode. There's no shame in it.
Go ahead and check this video for more info.
Part 3: Reconstruction & Expansion
My best advice for you when you're reconstructing the ancient city is to really analyze the vibe of everything around you, rather than the specific patterns. I've torn down multiple buildings and built my own themed ones in their stead because, truth be told, you're not going to have a good time trying to decipher anything but the walkways.
Always remember when planning builds that your floor is at Y=-51, or 13 blocks above the very bottom, but bedrock does start spawning at Y=-60, so you'll have about 8 blocks of clearance before it's poking into your builds. I'd recommend using normal deepslate to raise the terrain wherever you need to- it is a cave, after all. Cobbled deepslate, stonecutters, and spruce or dark oak are going to be your friends here, as well as collecting materials for soul lanterns and the like.
I would try making a part of the city that's sectioned off and intentionally left ruined, as well as building up some walls and guard towers to "protect" the city from the connecting cave systems.
Also, make a nether portal to the surface.
I don't have any more suggestions for you here- the sky is the limit when it comes to a space this free that's completely free of mobs, so I bid you adieu and happy building!