A video over 9 years in the making...
Every. Single. Retro Course theme in Mario Kart 8 Deluxe, with both their original versions and the remix version for comparison. Also including "guest course" remixes such as Hyrule Circuit and Yoshi's Island.

I tried to make sure all the volumes are relatively even, but if some of them are a little off, oh well. This video took way too long to make for such a niche premise, but I think it was well worth it.

Feel free to share your favorite / least favorite remixes down in the comments.

Timestamps:
00:00 Intro
00:09 Moo Moo Meadows
02:45 GBA Mario Circuit
05:04 Cheep Cheep Beach
07:55 Toad's Turpnike...I mean Turnpike (hehe)
11:19 Dry Dry Desert
14:24 Donut Plains 3
16:08 Royal Raceway
19:23 DK Jungle
22:09 DS Wario Stadium / Waluigi Pinball
24:51 GCN Sherbet Land
27:20 Music Park (or Melody Motorway. Yes I am American.)
29:29 Yoshi Valley
32:07 Tick-Tock Clock
34:29 Piranha Plant Slide (or Piranha Plant Pipeway)
37:10 Grumble Volcano
40:23 N64 Rainbow Road
44:30 Yoshi Circuit
47:36 Excitebike Arena
49:36 Mute City
53:48 Wario's Gold Mine
55:40 SNES Rainbow Road
58:07 Hyrule Circuit
1:00:21 Baby Park
1:04:19 Cheese Land
1:07:54 Animal Crossing
1:13:41 Neo Bowser City (or Koopa City)
1:16:10 Ribbon Road
1:18:37 Big Blue
1:23:00 SNES Battle Course 1
1:25:03 Luigi's Mansion
1:28:13 Wuhu Town
1:31:23 Urchin Underpass
1:34:54 Paris Promenade
1:36:43 Toad Circuit
1:39:10 Choco Mountain
1:42:41 YOU JUST GOT....
1:45:27 Tokyo Blur
1:47:45 Shroom Ridge
1:50:42 Sky Garden
1:53:00 Ninja Hideaway
1:55:33 New York Minute
1:57:59 SNES Mario Circuit 3
1:59:48 Kalimari Desert
2:02:48 Sydney Sprint
2:05:47 Snow Land
2:07:52 Mushroom Gorge
2:10:15 Sky-High Sundae
2:13:11 London Loop
2:15:45 Boo Lake
2:18:20 Rock Rock Mountain
2:21:13 Maple Treeway
2:23:57 Berlin Byways
2:26:35 Peach Gardens
2:29:05 Merry Mountain
2:31:59 3DS Rainbow Road
2:36:20 Amsterdam Drift
2:38:51 Riverside Park
2:41:14 DK Summit (or DK Snowboard Cross)
2:44:10 Yoshi's Island
2:46:46 Bangkok Rush
2:49:26 DS Mario Circuit
2:52:24 Waluigi Stadium
2:55:24 Singapore Speedway
2:58:03 Athens Dash
3:00:17 Daisy Cruiser
3:03:10 Moonview Highway
3:07:09 Los Angeles Laps
3:09:34 Sunset Wilds
3:12:24 Koopa Cape
3:16:20 Vancouver Velocity
3:19:17 Rome Avanti
3:21:32 DK Mountain
3:24:27 Daisy Circuit
3:27:14 Piranha Plant Cove
3:29:24 Madrid Drive
3:31:41 Rosalina's Ice World
3:34:09 SNES Bowser Castle 3
3:36:11 Wii Rainbow Road

This video is not monetized. Nintendo has rights to control over their properties and their music, so if they take this video down, it is what it is.