(Continued)

I found a shard in the left-side hidden room...strangely it doesn't seem this is required for the "Get all shards" achievement as I'd already gotten that to pop when I got all the ones in the previous DLC areas.

In the right-side hidden room is a double-handed weapon called the Shadow Blade which looks decent but has almost entirely dark damage. I don't see this listed in the guides here either but there you go.

I think I found one more shard in the Yellow section of the DLC's "Ghost World" map above.

There's one long horizontal corridor that has TWO hidden areas in the ceiling, one on the far right and one on far left. I'm pretty sure it's one of the rooms on the bottom of the loop on the left side of that yellow section. You can see the hidden areas briefly if you double-jump against the ceiling and I discovered it by accident since I often was double-jumping to fight the enemies there.

In either case, I was able to get into the rooms using the Espadon's R2 skill though I'd imagine the Claymore's move could work too.