The most important part of any racing game is momentum. The Kalimari Desert in Mario Kart 64 features one of the most annoying obstacles in the series, which hinders its momentum. The race track has a railway running through it, with active trains on the lines.
It is possible to
be stuck behind the train at various points in the game, which forces you to wait for it to pass. This will eat up all of the progress you have made against the others racers, and the rest of the track is empty and boring by comparison.
It bears mentioning that an updated version of the track appeared in Mari Kart 7. This iteration of Kalimari Desert improved a lot of the problems of the original, such as making the train shorter and adding ramps to the course. Shortcuts have also been added, which makes it possible to glide over the train, but the track is still extremely annoying for most players.