Moleville Mines is basically a large, dark cave. There is also a large mine cart ride where Mario can go and ride anytime after he beats the boss.
With the help of a few Monty Moles, Mario and his team head into Moleville Mines to find the next star. However, Mario jumps on a spring with a smiley face on it and is soon knocked out. After he wakes up, Mario spots Croco and his bandits up to no good. Mario defeats the bandits in his way and fights Croco. After a tough battle, Mario and his team defeat Croco and earn the Bambino Bomb. Mario uses the bomb to blow up a section of a wall to head deeper. Eventually, Mario, Mallow, and Geno find an odd character named Punchinello who doesn't want to give up his star so easily. Mario team defeats Punchinello (though he actually finishes himself off) and they earn the third Star Piece. Mario then heads further where he meets up with Dyna and Mite Mole where Dyna wants to go on a mine cart ride. Mario agrees to go with her and, after riding in the mine cart, crashes back into Moleville.