You should not need to grind this since it occurs naturally while playing the game, but if you wanted to you can save scum to speed up the process;
- Find a portal via world +2 select on Expedition or Certain Death difficulty, or find a Tome of Portal Traversal
- Save & Exit after standing next to the portal
- Reload your game
- Enter the portal, ensuring you get progress towards the achievement
- Exit to dashboard with
- Exit out of the game with
and selecting Quit
- Reopen Curious Expedition and reload your game
- Rinse and repeat entering the portal until the achievement unlocks