Beating The Legend of Zelda: Tears of the Kingdom without any kind of self-imposed restrictions is no easy task given the sheer amount of content available, but beating it without even visiting the surface of Hyrule? No, surely not, right..?
Well, that's apparently what Reddit user Black_Hand_Gotthard has achieved. As spotted by Polygon, they effectively managed to travel across the various Sky Islands by utilising Zonai Devices like the Glider and custom 'Airbike', rendering any requirement to land on the surface null and void.
In the above Reddit post, you can see that the player managed to reach the conclusion of the game without unlocking any of the surface maps. In addition to utilising Zonai technology, they also made liberal use of fairies to mitigate any fall damage while visiting as many shrines as possible to progress the story content.
They also managed to visit two of the four main temples, both of which happened to be located in the sky. Indeed, one of the boss battles normally requires the paraglider to beat with relative ease, but since Black_Hand_Gotthard was unable to visit the surface and obtain said paraglider, this made the boss significantly more challenging.
Of course, in order to actually beat the game, you need to go down to the depths below the surface. Thankfully, of course, it's entirely possible to go straight from a Sky Island and down into the depths without touching the surface, which is probably where the fairies came in handy. This can't have been easy, though, and we doff our metaphorical caps to such an achievement.
Coincidentally, it's also been reported by Nintendo Everything that the development team actually built the depths in "an extremely short period of time". At least, the core foundations of the depths were built remarkably quickly; actually fine-tuning the area and getting it into its final state apparently "took a long time".