Never played a Metroidvania? Then, a quick history lesson. In the olden days (aka the early 1980s) video games were typically linear and split into levels.
Then games like Metroid came along, offering massive interconnected worlds that you could explore at your leisure - as you hunt for upgrades and items that will let you bypass obstacles.
They're all about exploration, making maps (mental and paper ones), and soaking in the atmosphere.
They've fallen out of favour amongst the big publishers, but indie developers have kept the genre alive. And you can find loads of good'uns on Steam. Here are 14 of the best to get you going.
By Thomas Happ - buy on PC, Mac, and Linux (£14.99)
It's the game that inspired this list: a brilliant sci-fi romp that's heavily inspired by Nintendo's classic adventure. Only, with plenty of ideas of its own.
Like a mechanic where you can glitch enemies, as if your NES cartridge is a bit broken, to change their attributes. Or secret areas that are randomly distributed to every player, to make them truly surprising.
Ori and the Blind Forest
By Moon Studios GmbH - buy on PC (£14.99)
Ori is unbelievably gorgeous. Like a painterly Studio Ghibli movie that you can actually play. And almost as inventive, in its creative world and character design.
And while it starts off a bit slow, the game soon turns into a fast and fluid game of double and triple jumps, and bits where you grab ahold of enemies and projectiles in mid air and fire off in the other direction like a furry little rocket.
By Double Helix Games - buy on PC (£5.99)
Strider is a gorgeous and massive Metroidvania. But the real star is the combat, which is as frenetic as the best brawler.
You'll ricochet bullets with your sword, and do charge up attacks to slash through shields, and spawn a leopard to nuke enemy forces. And when every new upgrade adds to your combat arsenal, you'll be a crazy fighting force by the end.
By NIGORO - buy on PC (£3.74)
If you like Metroid games but fancy one that puts up a challenge, then this is for you. It's got all the exploration and upgrade hunting, but also a hefty difficulty curve that will test your mettle.
Bonus points goes to the art style, which deliberately makes the game look like an MS-X release. Makes a change from the usual NES wannabes.
Now Rogue Legacy is a bit different. It's quite definitely a Metroidvania (more Vania, than anything), with a big castle to explore and boss monster lairs to track down. Plus, skeletons. Got to have skeletons.
But it's also a roguelike so the castle design will shift around whenever you die. That might break the genre stereotypes, a tad, but it does mean you're always exploring something new.
By Housemarque - buy on PC, Mac, and Linux (£6.99)
Outland takes influence from a cult Japanese shmup called Ikaruga, in which you could switch between two colours to absorb two different types of bullet.
So you'll be swapping between red and blue to make platforms appear, obstacles disappear, and to fight enemies and solve puzzles. All within that classic Metroidvania structure.
One developer that loves this genre more than any other is WayForward. And its headline franchise is Shantae: a colourful cartoon adventure about a half-genie girl with whip-crack purple hair.
Pirate's Curse is an expansive Metroidvania with islands to explore and dungeons to delve into, and all the upgrades are based on a swashbuckling arsenal, like pistols, scimitars and cannons.
Guacamelee isn't afraid to talk about its influences. Chozo statues from Metroid show up in the game, and there are billboards with not-so-subtle references to Mega Man, Mario, Zelda, and more.
As such, this game has the structure of Metroid, the light/dark world of Zelda, platforming puzzles from Mario - but a feisty wrestling-themed fighting system all of its own.
Batman: Arkham Asylum
By Rocksteady Studios - buy on PC and Mac (£14.99)
This game proves that Metroidvanias don't need to be pixelated side-scrolling platformers. It's got an open world, upgrades that let you tackle obstacles, and boss characters in each lair. It fits perfectly.
And it's also got fist fights against goons, riddles and crime scenes to solve, and some of the best Batman gaming moments, ever.
Insanely Twisted Shadow Planet
By Shadow Planet Productions - buy on PC, Mac, and Linux (£11.99)
You never actually see your character in Insanely Twisted Shadow Planet, because you spend the entire thing inside a tiny tincan spaceship. You could be a shrew, for all you know. Or a bean with arms.
I digress. This is a wonderfully atmospheric entry in the genre with great puzzles and a physics system that lets you lift up boulders and chuck them around.
This one's more of a puzzler than anything, but the giant open world and the need to backtrack to earlier areas are clearly borrowed from Metroid. Not to mention the isolating sci-fi setting.
You won't be isolated for long, though. The game's all about making clones of yourself to solve increasingly complex puzzles. Soon you'll command a small army of yous, all working together to overcome obstacles.
Toki Tori 2+
By Two Tribes - buy on PC, Mac, and Linux (£1.19)
This cheeky Metroidvania is devilishly clever. Even if no one bothered to play it, and find out.
Instead of finding upgrades to unlock new areas, you instead learn more about how the world works. You can go literally anywhere at literally any time, but you probably won't until you figure out some new skill.
As they say: knowledge is power.
A Metroidvania needs a big, connected world to work. A space station, perhaps, or a medieval mansion. Aquaria finds its maze-like environment, deep beneath the ocean.
Here, as mermaid gal Naija, you'll swim about and beat up marine monsters. And you'll learn new songs to help you explore the world and overcome obstacles. It's serene.
By Nicalis - buy on PC, Mac, and Linux (£10.99)
It's often described as the game that kicked off the modern indie scene. A massive, involving, deep Metroidvania - all made by one dude in Japan.
The focus here is on fluid arcade shooting, as you spray bullets and switch between weapons in manic showdowns with crazed monsters. All with chunky pixelated graphics that remind us of the good old days.