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Mr. Mine Idle Underground City: The Complete Guide

Mr. Mine Idle Underground City The Complete Guide

Mr. Mine Idle is a popular idle mining game developed by Playsaurus that perfectly simulates the mining experience. Unlike other clicker games or incremental games, you either get rich or die mining.

Among many exciting features, the Underground City standout the most, as it’s one of the biggest locations you unlock in the game’s early stage.

This guide will show you everything you need to know about the Mr. Mine Idle Underground City, including how to unlock it, the features, and the frequently asked questions about this mysterious city.

The Journey to the Underground City

The Underground City is the 7th milestone in Mr. Mine Idle, unlocked at depths 300-303km.

By the time you reach this depth, a new icon with a pyramid appears in the right column. Like other game features here, this icon works as a shortcut, allowing you to quickly travel you to the Underground City with a single click.

The Underground City is a huge milestone in the game, as it unlocked several new resources and game mechanics. This includes:

  • Oil Pump and Oil
  • The Forge and Gems
  • Weapons
  • Monsters
  • and the Battle mechanic

Now, let’s go into the detail!

Underground City’s Key Structures

The Underground City has 4 clickable buildings: the Forge, the Pyramid, the Oil Pump, and the Armory.

The Underground City in Mr. Mine

Each introduces new mechanics to the mining clicker game, expanding the gameplay further and allowing you to vary the strategy.

1. The Forge (Shortcut: G)

The Forge is a medium house on the left with 3 big gems on top of it.

Within the Forge, you can craft 5 different types of gems using certain resources, time, and slots. And the Forge has 6 slots when first unlocked.

You can then upgrade the Forge to bring the slot number up to 50. However, doing so is not recommended as you don’t need this many slots.

The table below shows all the gems and their costs:

Red Gem2,000 Red Diamond10 Minutes1
Blue Gem10,000 Blue Obsidian
1 Oil
$10 Billion
30 Minutes2
Green Gem10,000 Coltan
10,000 Californium
4 Oil
$30 Billion
4 Hours3
Purple Gem25 Red Gem
25 Blue Gem
25 Polonium 2
16 Oil
$500 Billion
16 Hours4
Yellow Gem25 Red Gem
25 Green Gem
200 Oil
$1.5 Trillion
48 Hours6
Catalyst150 Uranium 2
75 Plutonium 2
4 Oil
$5 Billion
5 Minutes1

The gems here are then used to upgrade weapons in the Armory, which we’ll discuss below. On the other hand, Catalyst is used to reduce the forging time of a chosen gem by 20%, and this effect is stack multiplicative.

The Forge in Mr. Mine

This means you can apply multiple Catalysts in a single gem-forging task.

That said, using Catalyst on Green, Purple, and Yellow Gems is recommended.

Moreover, timelapses also affect the gem-forging time. So to maximize the efficiency, it’s advisable to regularly check the Forge after some usages of timelapses rather than using all timelapses at once.

2. The Pyramid (Shortcut: Q)

Once you reach the 300km depth and unlock the Underground City, you automatically unlock another 15 quests (or achievements).

The new quests can then be accessed through the Buff Guy at the top of your mineshaft or by clicking the Pyramid in the Underground City.

3. The Oil Pump (Shortcut: O)

The Oil Pump is located in the center of the Underground City, below the Pyramid. It has one and only one function, to extract Oil from the ground.

Oil is an important resource and is used for many upgrades, allowing you to progress deeper into the idle minibg game.

The Oil Pump in Mr. Mine

The Oil Pump can be upgraded through the Craft Center to increase the Oil Capacity as well as the Oil Extracting Time. When you first unlock the Oil Pump, it takes 7,200 seconds to gather 1 Oil and can only store 1 Oil max.

Overall, you should prioritize upgrading the Oil Pump, as it’s used in many other features in Mr. Mine.

4. The Armory (Shortcut: W)

Besides unlocking the Underground City, reaching 300km of depth also unlock a new game feature – Battles.

Monsters will regularly spawn at a random mineshaft, just like chests. And your mission is to click on the monster (with a red exclamation icon) to initiate the battle.

Yes, you guessed it! In order to battle, you must have weapons.

The Armory in Mr. Mine

Luckily, Mr. Mine provides you with a lovely Fist to punch the monsters lurking in the mineshaft when you first reach the Underground City. Later on, you can unlock more weapons by opening chests, killing monsters, and completing scientist missions.

Unlock weapons is just a small step; you need to upgrade them to become more powerful and easily defeat the bosses. That said, let’s come to the Armory, which is a mighty statue located on the right of the Underground City.

Here, you can use the gems forged earlier in the Forge to upgrade weapons. Each upgrade increases the damage and reduces the attack cooldown.

Strategic Guide for Navigating the Underground City

When you reach the Underground City, you may be overwhelmed with many new features simultaneously. So, here are a few tips to do as soon as you unlock the Forge, the Oil Pump, and the Armory.

You may want to save some resources, especially isotopes and Building Materials, to upgrade the Oil Pump. Then focus on forging gems to upgrade weapons.

While red and blue gems can be forged easily and cheaply, you want to forge a lot of them to upgrade the first level of all weapons. Later, you still need red and blue gems to forge other high-quality ones.

For higher quality gems (purple, green, yellow), remember to use the Catalyst to shorten the forge time.

As you can see, the whole rabbit hole in the Underground City involves upgrading the Oil Pump to get more Oil, constantly forging gems, and finally, upgrading weapons.

Once you have enough Oil and gems, it’s time to find more weapons.

Battle Feature in Mr. Mine

Try to open as many chests as you can, especially Golden Chests, as they have a higher chance of giving a new weapon. In addition, use timelapses to finish the scientist excavation mission faster, allowing you to pick excavation with a weapon reward.

In general, it’s recommended to upgrade weapons before battle to ensure victory. However, you can always test your limit by just fighting the monster, as losing in Mr. Mine doesn’t have any penalty besides the despawn of the monster.


And that’s all you need to know about the Underground City in Mr. Mine Idle.

Let’s now collect materials, forge gems, and upgrade weapons to conquer the mysterious mineshaft! Feel free to contribute to our community or Discord if you have any special strategies or questions.

Good luck exploring our idle mining games, miners!

Frequently Asked Questions

How Far Down Is the Underground City?

As mentioned before, the Underground City is located at 300-303km of depth.

How Does Oil Work?

Oil is another resource in the game, just like other minerals or isotopes. You get Oil overtime from the Oil Pump, which is unlocked at the Underground City. The maximum Oil you can hold varies depending on the oil pump level. So, to store more Oil, simply upgrade the Oil Pump.

What Minerals Should I Save Up for Underground City?

Overall, you should save all isotopes and keep at least 10,000 of all other minerals. However, if you’re running out of the storage room, here is the list of resources you should save for the Underground City:

  • Building Materials
  • Red Diamond
  • Blue Obsidian
  • Coltan
  • Californium
  • Polonium 2
  • Uranium 2
  • Plutonium 2

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