Pokémon Mystery Dungeon: Blue Rescue Team and Red Rescue Team/Fiery Field

After obtaining Surf and receiving the Clear Wing from Spinda, go through the great canyon to Xatu, who will tell you to go to fiery fields to find information on the mirage Pokémon. Now begins your quest for this Mysterious Pokémon. To enter Fiery Fields, you will need surf. You will also need to quick save.

The Dungeon
Fiery Fields is, the fifth hardest dungeon in the entire game. Fire Pokémon have regained their old glory in this game, and the field unleashes it all.

Boss Battle: Entei
On the 30th floor you will fight Entei. Once you defeat him, he will turn your clear wing into the red feather, and grant you access to Lightning Field, which is considerably easier than this.