Los Santos, San Fierro, and Las Venturas from GTA San Andreas. I loved to spend hours just exploring, looking for the secret items, and finding the funny little easter eggs and references.

The cities in Assassin's Creed. Can’t remember the names. Are they “big”? They seemed to be at the time. I only ever played the first game in the series; again, I loved wandering around and exploring.

Ark from Enderal

Vivec from Morrowind

maybe Washington DC from Fallout 3, depending on how you define "city"

The one that really impressed me was the capital on Kingdom Come Deliverance 2. At one point I was walking on top of the walls surrounding it and looking around for a nice screenshot and I was just in awe of how great that city was.

Paradise City from Burnout was pretty amazing, especially given you were supposed to navigate it at 250km/h. Lots of three-dimensionality about it too, with tunnels, overpasses, rooftops, etc.

Los Santos in GTA San Andreas. Heck, their versions of San Francisco and Las Vegas were awesome too.

Currently playing Project Zomboid and I know their Louisville Kentucky will be etched into my nightmares for decades to come, lol.

From a while ago I'd say GTA San Andreas, but I really want to shout out Boston from Fallout 4. It's easily the biggest city in a game that really fills out its size with interesting places and distinct neighborhoods. There's an amazing verticality to it as well in the central districts, and the mix of real historical buildings with new retro-futuristic ones is great as well.

Xenoblade chronicles X, especially back in 2014 on Wii U. But today it’s just middle sized - yet still created by hand and not procedurally generated.

Night City in Cyberpunk 2077 blew me away, its probably the most memorable location of any significant scale I've ever experienced in a game. I've experienced bigger, but forgettable, and equally memorable, but far smaller.

It's not big in an overall area sense but it's so dense that it can feel massive. Kamurocho from the Yakuza/Like a Dragon games. Seeing it evolve over 20 years in real time and about 35 years in game time has gotten me quite attached too. Each new game I do a loop to check what has changed and see if old friends are still there.

Bonus with having so much in game time in it is that since it's essentially just Kabukicho in Tokyo, all that in game exploring translates to the real world pretty well.

Paris from The Sabetour absolutely deserves a mention. It's a big city that you mostle travel by car, but it still feels rich and detailed on foot.

I imagine The Crew (2014-2024) somewhat qualifies - it's got the entirety of the US in its map. While its servers were shut down last year, it was just relaunched by the community a couple weeks ago

I'll always remember Night City. Over the years I've basically learned to navigate it without a map.

Holtburg in Asheron's Call there was a Tavern there that was a great hangout spot in Dekarutide

San Francisco from Watch Dogs 2 was great

I was going to say fourside, but you beat me to it, and the emptiness of it definitely played on the feeling of largeness.

There's also Castellia city in pokemon b&w, the people wandering and the 3d buildings made it look like a real city, alive and busy.

Idk if it counts, but in Professor Layton, when i didn't know what to do, i would desperately walk across the locations of the city and then realise it's quite big for there to be buses and streets.

Manhattan from TMNT Trouble in Mahattan on the NES.

Tp me Lindblum from FFIX felt really huge as a kid and it felt like there was so much to check out which i only noticed later.

The Imperial City from Oblivion was big-ish but not huge. Blackreach in Skyrim was big too, but stretches the definition a bit, because it depends if you count all the dungeons as expansions of the 'city', what with them being underground

The ones I actually remember in detail are the city locations from FF7: Crisis Core, Rogue Trader and Pillars of Eternity. Not sure why those three.

Britannia from Ultima Online

Agniratha in Xenoblade chronicles and Lazulis City in The Last Story, both are for Wii and both are great games Edit: I confused between Mechonis field and Agniratha.

The City of Paris in Assassin's Creed Unity was something. I mean that was impressive. City was huge felt very lived in and vibrant. Unity and to a lesser degree Syndicate were the last two Assassin's Creed games where the world felt vibrant. Partly because they did the walking tour bullshit and they killed the History part of the series. I mean I played a little bit of Valhalla and they just couldn't give a fuck anymore.

I realy like Las Venturas, GTA SA and the Hong Kong map of Sleeping Doge since it feels so alive and dense.

City of Heroes had some large areas.

i remember exploring potos in secret of mana either before they banished me for life just because a drink old man told me to save the town from a giant ant

The universe in Star Flight. Which fit on a 720k floppy disk. Nothing else has really measured up to that lost in a huge place feeling since.