Airports are near cities. Go do tourist things in the city.

If you enjoy adrenaline & frustration, Super Hexagon is one of those thumb-twitchy games that gives you the "just one more" impulse when you die. Unpossible is another.

Read webtoons!

Talk to people? Does the airplane have a bar? Even if you don't drink there's probably people there willing to have some conversations.

Put an alarm and sleep.

This is the perfect moment to write a short story

Fuck, I could use 20 hours where there's nothing that could guilt me into feeling I could be spending my time better than gaming. Go find a nice comfy couch somewhere and just veg man, enjoy your freedom from responsibility for 20 hours. Won't happen often.

I probably sound very traditional but… talk to someone? Make some friends? Call someone?

If you could get a rubix cube or something at the airport, (which seems plausible) could be a lot of time spent on learning how to do it if you download instructions beforehand.

Brotato, if you are using an android device.

https://play.google.com/store/apps/details?id=com.brotato.shooting.survivors.action.roguelike

Pretty sure your username is how you kill 20 hours.

If you truly didn’t enjoy Stardew Valley, then never mind ignore this. If you felt like it had potential but it just didn’t grab you, I’d suggest giving it another shot. It hooks some people immediately but it is a bit of a slow burn for others. It’s beloved by its cult following for a reason. But again, if you didn’t like it then that’s totally legit.

If you like puzzle games, The Witness is another exceptional PC game that was impressively preserved in its entirety when it came out on mobile. The visuals are stunning (though you may not get the absolute best experience on a small phone screen, but still) and it’s got a well-earned reputation for being one of those fully-suck-you-in-lose-track-of-all-sense-of-time games.

Buy a fat book.

It won't kill the full 20 hours, but 2 great mobile games that I like without the gambling bullshit: Vampire Survivors and Siralim Ultimate. The first one is free, so just try it. The second one is a monster training RPG where you can make sick combos and synergies.

If you can get an emulator on your phone you can play old games. Nealy endless hours of fun to be had. I recommend lemuroid and Legend of Zelda A Link to the Past.

Learn chess

I rarely play mobile games, but here's one that I quite like when I need to kill time or be active while media is in the background: Auralux 2.

I initially thought that the game wasn't properly weighted for difficulty, but then found that I just needed to adapt my strategy. I can complete most levels in 2-3 minutes, though some might take 4-7 depending on how it breaks (I play on the fastest setting after getting good at it on normal speed).

I pick it up when my partner pauses to get a snack, go to the bathroom, or take an important call. I can set it down as soon as she's ready because there's no real stakes; I'm really just competing with myself to score faster and faster "best" times. I also play it while listening to podcasts if I can't be physically active (or when I'm lazy).

I play on iOS. Not sure if it's on Android.

Duolingo. Then start texting your family in the new language that you learned that you forgot how to speak normally because of the delay time warp.

Hey, how did you get on? Hope the 20 hours passed ok and you had a good flight :-)

Baba is You. It is one of the best puzzle games ever made, and available on mobile.

If you're into metal/hardcore/etc at all, you should watch the documentaries Parkway Drive (Post-hardcore/metalcore band from Australia) has made, extraordinary stuff. This is the first one.

I also recommend chess.

If I had that long of a layover I'd leave the airport and go check out the city I was in. I had an AWESOME 12 hour layover in London once.

In case you get stuck again and need more games:

• DevilutionX (free, open source, needs gamedata) lets you play Diablo1 on Android, very good time killer (you might need to fetch the gamedata somewhere)
• Out There: Omega (paid but one time purchase) is a relaxed starship roguelite
• Battle For Wesnoth (free, open source) fantasy style tactical game
• Jagged Alliance 2 Stracciatella (free, open source, needs gamedata) - Jagged Alliance 2 on Android, tactical RPG, great timekiller like classic UFO or the old Fallout games.

Notable mentions: WorldOfGoo, Human Resource Machine

Go exploring. Walk the airport and go to other wings if it's a large airport. You might be able to find a luggage locker so you can walk without carrying anything.

In the same line, there are a lot of games that gamify walking. One. Two. The goal here is to exhaust your body a bit better for the 13 hr flight.

Learn something. A new language, maybe. A skill. Learn braille and go around the airport decoding the braille signs.

Do an airport scavenger hunt. Can you find yarn and maybe practice finger knitting? Maybe a deck of cards and learn some card tricks?

Talk to people. Honestly I'm an introvert so I rarely do this but it can be fun.

If you're the self-improving kinda person, I'd suggest looking up podcasts related to your line of work, hobbies, mind and health, psychology and that sort of stuff. Last time I went on a transatlantic trip, I stocked up on podcasts and took personal notes as well as notes for my private practice. Kept me engaged for a considerable part of it (total of ~22 hours), although without delays.

Makes you a bit more active even with passive media, and since you're working towards a goal, it also probably leaves you with a productive end result, be it for yourself or ideas for work, hobbies, etc. Couple of ones I like (as reference) are:

How to be a better human; Stuff you should know; Feel better, live more; Speaking of psychology; This jungian life

If you’re an iPhone user and intrigued by mobile games, go subscribe to Apple Arcade for a month. There are a ton of fantastic games without the bs freemium shit. Monument Valley and Alto’s Adventure (and their respective alternative titles) are great starters. I’m also a big fan of Good Sudoku which will teach you techniques to get better at solving them.

I’m sure you can get a lot better recommendations on current Apple Arcade games from social media or hopefully here on lemmy.