The Valley of Ends

It's looks like some kind of oak tree with a large hallow section to it. Even not seeing what nature of the tree, it's easy to tell someone's wrong with the tree. 

Does Fingolin see any other movement apart from the ghosts?

Perception: 20

He says to the others: "I could turn someone invisible to get a closer look at the tree, or I could send Ekkiwë and look through his eyes. Any other plans?"

There's nothing but the ghost as far as you can see as the party maintains a safe distance out of the clearing.

"So by the look of it, there is some kind of gateway, portal or summoning circle that gets the ghosts here. The Tree is the key. Either it is what summons those spirits, or it was what kept them sealed away, but got damaged. At least that would be my gues.

Can your familiar see in the dark? An aerial view may be usefull. "

How far are we from the tree? I assume within 60ft, so that those with nightvision can see whats going on. Is the wildlife still hidden? 

the clearing it pretty small in width, about 40ft across, the sole tree is about 25ft away from party who's at the end. Wildlife seem to be gone in this area, not muffled like before, just gone.

Looking at Resfaen : „I think you are the one among us who knows most about undead and spirits, do you sense anything?“

Salys will sit and stare at it for awhile before, "Alright, I'm going to enter the clearing a few feet, cover me?" And he'll move about five feet into the clearing and wait for any reaction.

As Salys moves closer, he hear something faint and abnormal for a forest but he can't place his finger on what the sounds is.

Resfaen will use her Divine Sense to see if this is something other than just ghosts and then try and think back over his studies if she has heard of anything such as this.

Religion: 10

Gotch sends his familiar up to scout overhead of the clearing.

perception: 18

Resfaen uses her divine sense, she gets what is best describle as a flickering sense of undead, one moment they're there, next they're not. 

Flying over head, the winged cat looks and sees the path of destruction of trees running through the forest continued for quite some distance, well beyond what it could see in the dark. 

"Is now a good time for a Fireball?", Fingolin whispers in jest, but his face is focused as he quietly follows Salys. Stealth: 16

„I‘ll have a close look at the tree, your cat should be able to watch me.  Once i‘m back i would say we follow that line of destruction to it‘s origin. What do you say?“

If there are no objections, i will sneak up to the two trees and have a closer look.

Sneak 18
Investigation 13 (perception +6)

Then i return to the others and report my findings.

Onyx carefully makes his way up to the tree but he hears that faint sounds that get earlier as he get closer. The party watches as Onyx's sneaky steps slowly become less stealthy and more almost zombie like walk as he approaches the tree. Before someone realizes something's wrong, Onyx holds up his hand to the tree and pass through the tree like an illusion but Onyx seems to pulled into the tree by his hand.

"Well that is not good."  Gotch says to the others.  "Seems like something took control of Onyx as they walked closer to that tree, then puff, they touched the tree and disappeared."  He glances to the others.  "Ideas?"

"I think we should hurry after him."

Fingolin plays a tune on the Doss Lute and he becomes transparent, then invisible. He draws his rapier and goes forward, intending to walk through the tree.

As Fingolin moves, he can hear the sound with his musically trained ears, he realizes it's some kind of music, possibility a piano similar playing through muffled. He feel a compulsion to come closer to the trees but he shakes himself free of its influence just short of the tree itself. 

Fingolin takes a moment to look closer at the tree, trying to find the source of the magic that tried to charm him, hoping to be able to shut it down.

Arcana:13

Investigation: 8

It isn't his field of study or any he has study but he has has touch it on passing but Fingolin think it's some kind of planar magics at work, phasing in and out of planes of existances and the tree is point where the connects the two planes and the music is coming from this point.