0.0.3 changelog:
+ Now works in multiplayer!
Each player can set their own custom spawn position (if you had a custom spawn position in singleplayer, you will have to set it again in this version), and all players will follow the rules set by the host (e.g. if CanEnterFromCave is false in the host's config.json, no one will be able to enter TCD while in a cave)
+ New variation: Sewer
* Replaced the tiles at the bottom of the Beach variation because they would get flipped incorrectly
* Rewrote location checks to fix an edge case where access to TCD would be incorrectly allowed
* You can no longer enter TCD while a dialog/menu/cutscene is being displayed (to prevent accidental entries while typing in a textbox, etc)

This mod adds a completely empty map, intended for storing lots of chests and machines. This means you can move all the boring stuff into here, and focus on making your farm (or your shed interiors) look nice and cozy, instead of just filling them with chests, crystalariums, or kegs.

You could turn your Chest Dimension into:

• A gigantic ancient fruit wine farm (of course)
• A processing facility for ores, quartz, animal products, trash, etc.
• A storage room where every item gets its own chest
• A remote storage network (when combined with the Chests Anywhere mod)
• A large area to dump your decorative items or rarecrows
  

You can go to (and get out of) the Chest Dimension with a single key (default: H). You can change the key in the config file.
If this feels too cheaty (for example, it could be used to quickly escape from monsters), you can edit the config file to not allow access from the mines, or to only allow access from specific locations (e.g. from your farmhouse).

Installation
Requirements: PyTK and TMXLoader.

• Download from the Files tab.
• Open the zip, and extract both folders into your Mods folder.
• Launch through SMAPI.
  

If you're installing the version with background variations: 

• Open the zip
• Extract the folder named 'The Chest Dimension' into your Mods folder
• Open the Variations folder
• Pick a variation, and extract it into your Mods folder.
  

(All background variations are interchangeable, and switching between them won't do anything to your TCD, other than changing the background.)

Configuration
You can change the mod's settings by editing Mods\The Chest Dimension\config.json.

TCDKey: Enter/exit TCD by pressing this key. (default: H)
SetSpawnKey: Set the spawn position (where you get placed when you enter TCD) by pressing this key. (default: J)
ShowEntryMessage: If set to true, shows a message in the chat when you enter TCD. (default: false)
EntryMessage: The message that will be shown.
CanOnlyEnterFrom: Only allow access to TCD when the player is in this location (possible values: Farm, FarmHouse, Town etc.) Set to 'null' to allow access from everywhere. (default: null)
CanEnterFromCave: If set to false, you will be unable to access TCD while inside the mines or the Skull Cavern.
ShowCannotEnterMessage: If set to true, shows a message in the chat when you try to enter TCD from a disallowed location. (default: true)
CannotEnterMessage: The message that will be shown.

Source
Here, look at my awful code: https://github.com/cilekli-link/SDVMods/tree/master/TheChestDimension