Doga's Manor is only accessible with Nautilus, this is why you have to go back to Ancient Ruins to pick it up. Then come back to Doga's Manor.

 *** This dungeon is a one-time visit so make sure that you collect all chests and bestiary list and chests.

Chests (8):

• 10000 gil (x2)
• Rising Sun
• Lust Dagger
• White Musk
• Chocobo's Wrath
• Phoenix Down (x2)

Monsters:

• 155. Peryton
• 156. Ogre (missable)
• 157. Cyclops (missable)
• 158. Nemesis (missable)
• 159. Humbaba (missable)

There are 2 bosses here (Doga and Unei) which you have to fight one at a time.