This U-Bahn puzzle is named after the train in Paper Mario: The Thousand-Year Door.
If you are unfamiliar with U-Bahn, here is a guide that covers the core logic.
Draw a loop network through the centers of some cells, which may branch or turn, but may not have any dead ends.
A clue outside the grid indicates how many times the corresponding line shape (i.e. a cross, branch, straight line, or turn) appears in the corresponding row or column, irrespective of the line shape's rotation.