Ice Land

Ice Land (alternatively Iced Land, Winter Wonderland, the Ice World, or Ice Country ) is the sixth world in Super Mario Bros. 3. It is the largest world in the game, with ten levels, three Hammer Brothers, three fortresses, three Spade Panels, two Toad Houses, and a castle that has been taken over by an airship. As the world's name implies, it is a frozen wasteland covered with slippery floors and frozen lakes, with many structures and platforms made of Ice Blocks in various sizes. Lemmy Koopa takes over this icy kingdom by stealing the royal magic wand and turning the king of Ice Land into a seal (a Monty Mole in the game's remakes). The map in Super Mario Advance 4: Super Mario Bros. 3 shows that Ice Land is north of Dark Land and east of Pipe Land.

The Adventures of Super Mario Bros. 3
In The Adventures of Super Mario Bros. 3, Ice Land, though never referred to as such, only appeared in the episode "Life's Ruff" (which is the only episode where this world is shown as the title card), where it had a different ruler named King Windbag. He bullied his servants and never said "please", but when Hip and Hop came, they stole his wand and turned him and Luigi into dogs and harassed them for a bit, but were eventually defeated and returned to Dark Land. The castle is depicted with igloos around it.

Super Mario World television series
An icy tundra, referred to as "Ice Land", appears in the first episode of the Super Mario World television series, "Fire Sale". Here, it is under the control of Kootie Pie, who had stolen Mama Fireplant to make it warmer. However, Ice Land began to melt because of the heat, and Mario, Luigi, Princess Toadstool, and Yoshi arrived to save both Mama Fireplant and Ice Land.

Music
An arrangement of Ice Land's map theme, "Slowly, Slowly", plays in Mario Party during the Pedal Power and Ghost Guess minigames. A more faithful arrangement plays whenever Mario receives anonymous e-mails in Paper Mario: The Thousand-Year Door. The map theme's melody is incorporated in Super Smash Bros. Ultimate into the "Fortress Boss - Super Mario Bros. 3" arrangement alongside the map theme for Dark Land and the titular Fortress Boss theme.

Trivia

 * This is the only world of the game that is possible to go backwards from using a Magic Whistle, as using it in the sixth world will allow one to return to the fifth. However, in Worlds 5 and 8, using it can cause one to return to the current world.
 * In Super Mario Advance 4: Super Mario Bros. 3, the path to the second Toad House is altered so that it is accessible at the fork after World 6-4 instead of only accessible through World 6-5.