I'm a portal, small and deep, A guarded secret I keep. Though round or square, my form may be, What must be found, to look through me?

I am your key. There are many like me, but this one is yours. I'm not usually metal, nor do I fit into a lock. You can use me to get in, but usually just once.

Hang me right, I'll see you through, I'm also nailed for protection. As in form, I am shaped like you, Can you beat this misdirection?

Too much of me and I'll make you wince. You'll do the same if you find a party of me. Despite that, I'm often A favorite of the masses. Squeezed and mixed, I play nicely with other flavors.

I stretch through space, yet hold things tight, a cosmic spiral of distant light.