Mario Circuit - This track features Peach's famous castle and shows off some of Mario Kart 8's antigravity sections. The only secrets here can be achieved my using a mushroom to cut corners over the grass!
Toad Harbour - Mario Kart 8 pays tribute to San Francisco with this level by the bay! Here you can use a mushroom to cut the first turn, just watch out for that box and the last turn, but watch out for the trolley. There is also a small alley at the end of the race on the left, take it to skip one of the upcoming turns!
Twisted Mansion - The track has multiple sections, including a main house area with two levels, the top one of which can only be accessed via glider, a library with sharp turns, an underwater section, and a garden with statues that try to hit you with axes. There are two mushroom-accessible secret areas: after the first Anti-gravity section, use a Mushroom to cut through the hallway on your right and on the last turn through the grass.
Shy Guy Falls - These mining grounds actually has four areas where you can use some tricks to get ahead with! You can shave off a few seconds on the second turn by using a mushroom through the grass, you can also aim for a higher track after entering the gliding section. After this section you can use a mushroom to take a track on the right and skip a big turn, and then skip over the grass on the last turn too with a mushroom.