It might be a bit too on the nose for IC but Chrono Trigger Corridor of Time is pretty deeply embedded in my brain.
https://youtu.be/2XSFVlUM08s
i‘ve been trying for days to think of something else, but i’m stuck on mario 3d world for this one.
https://youtu.be/Mz0Sq4XdvoA
and the last one is a two-fer:
https://youtu.be/e3cxGIppPiM
i *love* the _mario galaxy_ space castle theme.
We do not have enough Mega Drive tracks in here.
Of course Shining Force II the greatest game ever conceived has a ballin’ overworld theme, Wandering Warriors, which doubles as one of the earlier battle themes in outside environments.
The same composer Takenouchi Motoaki also composed the soundtrack of Landstalker and I guess Ryle’s theme / Nigel’s theme qualifies as the standard overworld theme of the game.
But the one I really want to highlight here is Phantasy Star III’s ground theme by Takeuchi Izuho. Like many aspects of the game (the generations system etc.), the soundtrack went for something pretty unique and innovative even if the result possibly did not match the intent. The game’s overworld BGM starts with a pretty simple (and mediocre) two channels-wide track, which probably left a poor impression on people who checked the game but didn’t go far into it. The secret behind this strange tune is that each additional party member adds a channel and instrument, progressively revealing the real overworld theme. Here’s a nice little mix that links the different variations in sequence. The second version of the theme kicks in at 0:49, the third version at 1:37, the fourth version at 2:26 and the complete version plays proper from 3:15. It’s a pretty neat idea!
I love that concept! A similar idea showed up in two of my favorite games: Outer Wilds and Breath of the Wild
I really wish I had more knowledge of Genesis/MD RPGs to help contribute, but I figured I would at least toss in this jaunty little track from Crusader of Centy:
This song came to mind…
https://youtu.be/DHvr6ZB6Flg?list=PLEUMLboERIGcz0XYETsaCSwaE3uWiKs58
It's from one of the later PS2 RPGs, Mana Khemia 2. Halfway through the game or so, the overworld map changes to this one. Reminds me of my dad karaoking in parties back when I had little birthday parties. When I first heard it, I would just leave the game on too and blast it so my family could hear it because I always feel like my family would like the song. They never commented on it though.
Wild Arms bonus round 
https://youtu.be/joq9WadIMxE
https://youtu.be/In68Dk6EIek
https://youtu.be/o8njv_kH5qs
https://youtu.be/e9chSZuGHUM
I agree w/ Exodus that I really like a good driving overworld theme over the more majestic ones (which still have their time and place of course.) I think the ones that come to mind that haven‘t already been mentioned here are the tracks from Secret of Mana by Hiroki Kikuta for when you summon Flammie and take off - Flight Into the Unknown and again once the Mana Fortress is summoned - Prophecy The urgency is really there in this track! (Though I’d just sit there and listen to it for long periods of time in game…)
I'm also not sure if it counts as overworld or not but the one track from Ar Tonelico that always sticks out in my mind when I think of that game (aside from the OP) is [Overcoming the Trials](https://www.youtube.com/watch?v=kdIbaKO_fuw) (@ 19:02 here)
I'll have to kick this around a bit more and see if any others float up from my playlist
Yes, this is one of the few tracks where I actually enjoy the Arrange Mix from the Brink of Time as well. (Especially @ 1:28/1:30) I'm constantly having to remind myself that track was worth the price of admission for the CD. (The rest of the album is pretty meh IMO…)