World 3-1 is a relatively straightforward level with many pipes. Some pipes contain Piranha Plants, while others can be entered. There's a hidden 1-Up Mushroom in a block near the beginning, above the first set of two '?' blocks. Jump on the rightmost '?' block, then jump again to reveal the 1-Up. Further along, you'll encounter a series of pipes that form a small maze. Most of these pipes lead to coin rooms, which are great for racking up points and extra lives. The main path continues to the right. Be mindful of the Goombas and Koopa Troopas patrolling the ground. The flagpole is at the end, as usual.
