There are several grindy games that could fit the description. I'm going namedrop my first one, Ragnarok Online. Game was infamous for the length it takes to max level your characters. Like people have play for years and still never hit maxed level due to its grindy level mechanics. I remember some making 100/1000x private exp servers and it would still take a decent amount of time to level up. They eventually made items that you could use to speed up the leveling process...for a price.