World 6-Fortress 1

 1 is the first fortress in Ice Land from Super Mario Bros. 3, and the fourth level in the world overall.

Layout
The level starts with a roller coaster platform, and a few Roto-discs and Lava Bubbles. In the beginning, there is a Super Leaf, which the player needs to collect fast or they lose the roller coaster. Next, there is a door which leads to a room with another Super Leaf, a Super Star, and more Roto-discs. Next, there is another door which leads the player to the boss - Boom Boom.

Enemies

 * Roto-discs
 * Lava Bubbles
 * Boom Boom (boss)

Level statistics

 * Power-ups: 3 (two Super Mushrooms or Super Leaves, and one Super Star)
 * 1-Up Mushrooms: 1
 * Secret areas: 0