BoTW/ToTK & Xenoblade X. Nothing comes close. Very organic horizontal merged with vertical. 

BoTW was pretty good if only the stanima meter was double the size, it really hurt exploration in that game. Haven't played ToTK but I've seen enough to know it is probably a fantastic map, taking BoTW and then adding Skyward Sowrd like verticality. I do wanna play it. 

You can make your Stamina gauge double and triple the size

With full stamina and the climbing gear you can climb really high. Also there's plenty of slightly angled terrain where you can recover stamina and that's not going into having stamina food .

I suppose so, it'a just kinda anxiety inducing with that meter but aye, maybe that's the point.

I'm going a bit retro with Earthbound. The map is stitched together, incomplete, and very much not accurate given some of the journeying you see in the game... but you get the point:

For open world games, Xenoblade Chronicles X, Breath of the Wild, and Witcher 3. All three have their different strengths.

This, Xenoblade's worlds are unforgettable and the first game in particular blew my mind back in the day.

Breath of the Wild is also one of the greatest for its organic untamed wilderness and sense of nature and scale, plus how great it feels to explore and overcome its challenges.