To use the mod, hold down the modifier key (default Left Shift) while clicking on the main stairs in a mine level, the door in Skull Cave, or the stairs in the mine entrance. This will open a small menu in which you can input a mine number via the keyboard. Press Enter to travel to the typed floor. Press Backspace to delete a digit.
By default the mod restricts travel to floors you've visited, but you can remove this limit in the config.
Technical
Requires SMAPI, uses Harmony.
Compatible with Mod Updater for automatic updates.
Implements a Generic Mod Config Menu interface to change config settings in-game.
Code is at https://github.com/aedenthorn/StardewValleyMods.
If you want to complain or ask for help or help me test my mods, you can visit my Discord server.
A list of all my mods for Stardew Valley is available at https://www.nexusmods.com/stardewvalley/articles/895.