Pokémon Mystery Dungeon: Blue Rescue Team and Red Rescue Team/Solar Cave

After beating Rayquaza and the credits roll you should have access to Solar Cave. Getting in will require the HM Dive, but Wishcash will give you one.

The Dungeon
On floors 1-14 you should find a key. On floor 15 there’s a chamber with a link cable, dive, or waterfall in it. On floor 20 which is the last floor you could find surf or a link cable on a platform surrounded by water. Bring a water-type or a floating Pokémon to get it. On floor 10 there's a locked chamber.

Items

 * Keys
 * Moon Stones
 * Sun Stones
 * On B10F: HM Dive
 * On B15F: HM Waterfall
 * On B20F: HM Surf or a link cable