Copy the images and place them in My Documents/Dolphin Emulator/Load/Textures/GTSE4F.

To enable the Gothic Tileset in MapMaker, enter this Action Replay code:
G2EB-VKHJ-1JXVF
1XZ1-K0KJ-HMD2E
It is called "4" in the Tileset select option.

Due to issues with the lighting on the tileset's doors and windows, they will appear bright white while this mod is active.