You should not need to grind this since it occurs naturally while playing the game, but if you wanted to you can hold out near a corrupted mountain as Spiders endlessly spawn to attack you. This also means you could have an infinite fame or fortune source if you continuously wait near a golden pyramid or the ship.
Note: Giant Spiders (and polar bears) have only one attack die, meaning you can stun lock them to death with a mind/maneuver combo or an eye/mind/hand combo for multiple enemies and wailing on them with any leftover dice.