Echo Stone
From SpiralKnights
An Echo Stone is an artifact found in The Sanctuary. It is a remnant of a message, left by an unknown entity, for any Knight who would brave the Unknown Passage.
There are four Echo Stones, one for each Shadow Lair. The echoes they contain can be listened to at any time after obtaining them.
This page is about to be loaded with spoilers, so please, don't spoil yourself if you don't want to.
Gloaming Wildwoods
I dream... Within my dream, I saw it open the void, felt its endless hunger. You are safe here, Knight. Within this dream, its many eyes cannot see you nor can its many arms reach you. But this dream is fleeting. Use what is here to prepare for the battle to come. It knows of you now. It will find a way out and come for you.
Royal Jelly Palace
Working on it.
Iron Munitions Factory
This one, too.
Firestorm Citadel
And eventually this.