You might spot the Kloros Guild pretty early on in Forspoken (opens in new tab). The entrance is high up on the side of the tower, so there's no way you'll reach it by conventional means. You'll find the guild in Middle Praenost fairly early on in Frey's adventures across Athia.
Guilds generally contain useful items, so they're worth exploring if you can find a way into them. They can also house enemies, so you should be prepared for a fight once you find your way inside. Unfortunately, you won't be able to gain access to the Forspoken Kloros Guild until you have a particular skill unlocked, so here's what you need to know.
Forspoken Kloros Guild: How to get inside
First up, you'll need the Zip ability, which is rewarded after you defeat the first main boss, Tanta Sila, in Chapter Five. With the skill learned, you'll gain access to many previously inaccessible areas, including the Kloros Guild tower.
Once at the Kloros Guild, look for the huge rock formation nearby with golden crystals attached to it. You can use your newly acquired Zip ability on these to propel you to the top of the rocky outcropping. Once you're up there, look back towards the tower to see the flat-topped rock just to the right of it.
Jump across to this conveniently placed platform, and you should see that you're practically level with the doorway into the tower. Now it's just a case of jumping and grappling across. If you're having trouble seeing where you're meant to go, this video (opens in new tab) should help direct you.
Once inside, make your way down several flights of stairs and defeat the Nightmare enemy on the bottom floor. You'll be rewarded with Decay Nails for taking it out.