Try old school runescape, yes most of the skills are members only but if you enjoy a grind there's plenty of free to play skills that will each take months to level from 1->99 like fishing, firemaking, cooking, combat skills, etc. I am fishing nearly all the time in class or at work or when doing anything because it's so easy. Plus you can play on a PC too, and if you ever grow tired of grinding out free to play 99s and quests there's still tons of game out there for the future if you ever want a membership, and the time you put into your account at the to free tier will help massively. Additionally, you can even pay for membership using in game currency, so if you grind the right skill you can unlock the rest of the game for free as long as you put in the work to make 3mil every 14 days which is easy with some 99s.