World 3 is one of the two worlds after World 2 and leading to World 5, likely being the one you clear first since it is easier to unlock. The theme of this world is beaches and water, although not every level is based around it. Particularly notable is the Ghost House, which should be the first one most will encounter on a normal playthrough. There are only one of each Toad House, while any secret paths branch away from the main route more.
- Around where the Cheep Chomp first appears, there is a green Warp Pipe sandwiched between a red and a green pipe that spews produces currents. Go through the Warp Pipe to enter a small area with the Star Coin.
- This coin is plainly visible between two water-spewing pipes, but the Cheep Chomp nearby may pose a danger.
- The coin is surrounded by blocks a bit past the P-Switch. Hitting the P-Switch is the safest way to obtain it.
- The coin is surrounded by blocks. Have a Skeeter break the blocks to obtain it.
- This one is airborne. A dashing jump will barely let you get it, but you can use the Koopa or Skeeter for a boost.
- Go into the first of the two ceiling pipes after going through a horizontal pipe. As Mini Mario, run across the water and jump in the middle of the bonus area to collect the coin.
- In a bonus area accessible from a pipe soon after the checkpoint. Do a well-timed jump on the moving mushroom to get it.
- Use the second set of scale platforms to reach a high up ledge, where the coin is located.
- In the air above the final abyss. The moving mushroom makes it difficult to collect.
- When you first see this coin, it is inaccessible. Go down the first red warp pipe after seeing the coin, then go to the left of the secret area and take the red pipe up to collect it.
- From the pipe to the left of the middle checkpoint, wall jump up the gap between the two pipes to reach an area supported by a tiny pipe where the coin can be found.
- Out in the open near the flagpole. The only obstacle here are some dangerously-placed Piranha Plants.
- The coin is on a platform below a tall bridge. Stand on the falling platforms to drop down to it.
- You'll need to swim in the water for this one. While evading the Spike Bass, wall jump up the two stone platforms surrounding the coin to obtain it.
- After hitting the P-Switch, quickly follow the trail of coins to a red pipe. Jump into it and stay on the platform you emerge out on to drop to the coin.
- From the first cannon pipe, fall to the lowest fence and climb to the left. Climb up the next fence to get to where the Star Coin is.
- After switching sides on the fence for the first time, move around the Amps to the left and switch again. Go up, left a room and up a room to reach the Star Coin in front of a fence.
- In the first section, you want to take the rightmost door. In the area it leads to, press the red switch and quickly move up to get to the door. The Star Coin is right next to it.
- Sink down upon reaching the first gap in the floor. A Star Coin is located here, guarded by a single Blooper.
- After the red ring is a series of pipes. Go through the second one from the left and swim to the bottom-right of the area you're sent to. The coin is there for you to collect if you can dodge the Bloopers in the way.
- Below the exit pipe pointed to by the sign, fall down the gap to get the Star Coin at the bottom. Start swimming up once you do, as some Bloopers will ambush you right after.
- Behind the door beside the second P-Switch is a room with the coin and some Splunkins. Bounce off a Splunkin to get it.
- After pressing the second P-Switch, go up the staircase and jump to the other staircase as soon as you can. Get to the top of that staircase for the Star Coin.
- You need to be Shell Mario for this. Before going into the exit door, make a Shell Dash to the right to break some blocks in the wall. The Star Coin can be found behind it.
- In a small pocket right beside a Skewer. Watch out for that Skewer when grabbing it.
- After the donut lift, jump to the rope and swing left to the ceiling. Go left to get to a Star Coin that could be seen but not taken earlier.
- To the right of the double doors is a small gap. One last Skewer is beyond that gap, as well as the coin. Time your jumps right so you can leap to the ledge with the Star Coin.
On the first erratic-moving mushroom, you might notice a set of pipes while crossing the wide pit. The pipe you want to go down is the green-colored one at the right, which takes you to a secret area with a P-Switch and a Spin Block. The P-Switch creates a ton of silver coins that you can use the Spin Block to collect. After you're done, go down the right pipe to reach the flagpole area. You must hop across some more tilting platforms before you get to the pole.
Going through this exit leads you to World 3-B, a level which continues the athletic challenge and which can act as a major shortcut across the world.
You can access this secret exit once you get to the third P-Switch, which is the one required to make the hidden door appear. While one did appear close by the moment you hit the switch, there is in fact another hidden door that the switch reveals. Once you hit the P-Switch, immediately run up the first set of stairs, then jump over the gap and fall down the stairs to the left. The hidden exit is to the immediate right of the second P-Switch. Outside, wall jump off the left set of blocks to get to the horizontal block platform. Jump from there to the red flagpole.
Going through this well-hidden back door takes you down a path to the World 3 Cannon. The cannon launches you high above sea level to the rocky peaks of World 6. Watch out for the hike in difficulty!