Much of the fort's structure is decayed, with broken doors and missing roofs, though its main walls still stand. The main gate leads north across a wooden bridge to the path up towards the Manamia Trail - the Ruin also has exits to the east and west.
The bandits have made camp in the castle's outer ward, and gather there at night. They can also be found on the main and side towers standing guard.
There is a jetty on the coast which can be accessed by a steep track from the castle.
The bandits, led by Maul, each have names derived from weapons. They are Anelace, Basilard, Caravel, Claymore, Culverin, Falchion, Glaive, Hammer, Lance, Mace, Mercygiver, Pike, Ranseur, Sling and Voulge.
A considerable quantity of Cloudwine may be found in breakables throughout the castle, and there's a Ferrystone located on the tip of a boat at the jetty. A Wakestone Shard may be found atop the remnants of the southwestern lookout tower facing the sea. A small unassuming crate at the centre of the southeast tower, accessed by levitation from a nearby broken wall may contain Stone-Moss Poultice, Balmy Perfume or a Large Coin Pouch.
- Salomet's Grimoire may be found at the highest point of the castle. Under certain conditions, such as when attacked, the bandits will hide the chest.
- A chest by the stairs leading to Salomet's Grimoire may contain Bandit's Mask, Ebon Neck Wrap, Dusk Shoes or Gossip's Mask.
- Chainmail Bracers, Weak Guard or Hunter's Jacket atop a lookout tower overlooking the main northern entrance.
- Wyrmward Perfume in a chest next to some boxes on the ramp going from the outer ward to the main tower.
- Red Leather Armor, Bandit's Glove, Rose Ring, or Ring of Gules - in a small room within the castle's eastern walls.
- In the larger square room in the ruined tower keep: either an Incognito Mask (common), or a Large Coin Pouch.
- A Hero's Worth - kill 35 male bandits
- Reclaim the Roads - kill 10 bandits
- Thick as Thieves - kill 10 male bandits for Ophis
- A Troublesome Tome - obtain Salomet's Grimoire
- Smells Suspicious - obtain a vial of Wyrmward Perfume
- No Honor Among Thieves - complete tasks for Maul
- Badge of Vows 67 - on the castle outcrop
- Badge of Vows 79 - on a castle tower
- "It appears to be a bandit hideout."
- "I feel half a thief myself, sauntering through this place." (a words of hypocrisy from the Pawn)
- "Thieves or no, we've naught to gain from unnecessary combat."
- "Mind your steps, Master. This fort holds many twists and turns."
- The bandits at Aernst Castle are much like their counterparts, the female bandits at The Ruins of Heavenspeak Fort, and will not normally attack the Arisen unless provoked.
- When provoked they will tell you to "Bogger off.", "Piss off." or "I'll bleed you dry.".
- The Ruins of Aernst Castle (Capcom, YouTube)