Head West after the gate and into a hidden room, then go into the portal. Once inside, search for the Red M. Key found in the blood stained floor North-West of this room.
Use this key to enter through a gate to the East of the room to discover the Undead Dragons.
|Dead Dragon Egg||1||1/100|
|Green M. Key||1||1/50|
|Empty Chest 2||1||1/(?)|