Created by Evil Blunt, which I'm certain is their given name, Red Dead Freecam is a mod that lets you fly around Rockstar's immense slice of the Wild West. There's a great photo mode in the PC version of Red Dead Redemption 2, but you can only travel so far with it. However, with this you can move freely around the entire map—including parts you were never meant to see.
It's a great way to appreciate the scale and beauty of the world and it's remarkable how good the game looks even when you're 40,000 feet in the air. You can download the mod at Nexus Mods, as well as Red Hook 2, which you'll need to run it. Just make sure you don't try and use it online or you may get banned. Rockstar is cool with mods as long as you only use them solo.