This level itself is inhabited by ten Goombas overall, and four Koopa Troopas, two red and two green. As it is the first level in the game, these enemies are introduced to this level. As a background element, Princess Peach's Castle can be seen from the beginning section of the level before the first ledge. The terrain of this level is grass-themed with several slopes and Warp Pipes. You're also able to see yellow hills in the background.
When Mario starts the level, he must walk towards three Question Blocks, one with the other two not connected to it and the other two connected to one another. The second block contains a Mushroom (Fire Flower, if Super Mushroom is powered already). Also, the very first obstacle in the game is underneath these Question Blocks; a lone Goomba on which Mario must avoid. Then, there is a group of three coins which can be collected, and another three, making six total. Then, there is a lone brick on the top of the ledge which contains a single coin inside of it. Down the ledge is a group of three connected bricks, the center one with a lone coin and a lone brick atop the three in midair (containing multiple coins, maximum of fourteen total). Then, there are four more coins for Mario to collect along with another Goomba with Warp Pipes to his left and right. Then, the first ledge in the game can be seen. This ledge must be jumped across and can be considered simple, due to it being small. There is another group of four coins above it.
On the next section, there is a Mega Mushroom inside a lone Question Block, which can be used to scavenge through the level easily. Though it is an optional element to the course, but makes the course easier. There is also another pair of bricks in three, the center having a Question Block, along with the third Goomba in the level underneath the pair of bricks. Two more bricks connected together can be seen, both contain a single coin and a coin group of four can be seen above the second ledge after the two connected bricks. There is also a pipe next to the ledge. Then, there are three coins that can be seen next to the group of five bricks in the air, after the Warp Pipe and the first Star Coin even higher and next to it. The first and third bricks contain a coin, while the second contains a Mushroom or a Fire Flower. Beneath the pair of five bricks is the first green Koopa Troopa in the game. Then, there is a red Koopa Troopa on a pair of nine bricks, the third containing a hidden star above it. This pair is divided into three and split into sections, one section on the top. There are also three hidden blocks that give out a single coin at the bottom. There is also a coin in the third and seventh visible bottom bricks. The center-top has a beanstalk leading to an option secret cloud-themed area with a Red Coin Ring in it where eight Red Coins can be collected for a Fire Flower or a 1-up Mushroom. Also downwards, there are four coins leading to the bottom.
If not, Mario must continue a few steps to the midway point directly after the Warp Pipe leading to an optional underground area. In this area, there is a lone Goomba at first with five coins above five bricks. There is also a hole with four coins above it, like always. Then, two Question Blocks on the sides with three bricks used to connect the Question Blocks together with the bricks used. The fifth brick contains a Mushroom or a Fire Flower and the first and third have a coin. There is also a Warp Pipe leading out of the area with the third Star Coin above it and a formation of four coins on the left of the pipe.
If this area isn't chosen, Mario must continue along where there are three lone bricks not connected that all contain a coin. Another Goomba can be found beneath these bricks. Then, there is a ledge which Mario needs to jump over and is rather more small with another four coins above it and a Question Block after it containing a Mushroom or a Fire Flower (depending on the form) and another ledge, step-formation style with another Goomba walking down it. Then, there is a small hole with three bricks enclosing the second Star Coin below it. Super Mario or Fire Mario forms are required to get it as small Mario cannot destroy bricks. Another Goomba can be seen next to this brick-enclosed hole, along with a Question Block containing a coin aside another ledge with a hole next to it. A Goomba can be seen next to a hole with a Warp Pipe dividing the two nearby Goombas. There is also a group-of-four connected bricks, the fourth containing a coin. Next to these bricks is a single Goomba and green Koopa Troopa, along with a nearby ledge with the only formation of three coins in the level itself. Then, the final brick formation in the level is encountered with a red Koopa on top of the bricks, the third brick having a lone coin and a hidden star above the bricks. Then, Mario must go up a stair of blocks, like in the original Super Mario Bros. to reach the flagpole in order to complete the level and move on to World 1-2.
- Star Coin 1: In plain sight after you get the Mega Mushroom
- Star Coin 2: In an underground area which can be accessed via a Warp Pipe next to the midway point of the level. The coin is in the top-right corner of this room.
- Star Coin 3: In a gap after the midway section with a hole splitting the two areas, blocked by three bricks on a ledge. Small Mario cannot obtain this coin.