Battle the first of many Alonne Knights and find the Twinblade +7.
Go through the hallway and kill your first Alonne Knight. Now before you climb the stairs use ranged attacks on the Demon Frogs in the alcoves, or use the passages either side of the room to melee attack them. In the middle you'll find five Smooth and Silky Stones, three Human Effigy and a Skeptics Spice.
To the left of the top of the stairs is a passage where you'll find a Rusted Coin at the end. Two more Alonne Kinghts attack from the room at the end and there's more Demon Frogs in the alcoves of that room. Go down the next hallway to circle back to the first room.
Go right to fight another Alonne Knight and finish off any frogs before going to the left hand passage and killing the demon frog that blocks your path and the Alonne Knight. Drop down through the hole.
Follow this hallway into an open area where five knights await. Move slowly and and they won't all attack at once, allowing you to have a bit more of a fair fight. At the end of the room is three Repair Powders and five Radiant Lifegems.
Head down the stairs on the far right and go right at the intersection and you'll find a Twinblade +7. Drop down to the room ahead and kill the Demon Frog on the right. On the far right there's another room with an Alonne Knight in it and a path to the Demon Frog you just killed. The left hand path features two Alonne Knights. Go down the path and up to the main room. head left into the hallway and down the stairs to see a mist door, which will take you to the boss battle with Sir Alonne.