The Portal

A mirror topped with the Bi-sected Circle Sigil, tall enough for a man twice your size to enter - it's surface smooth, unbroken by any minor defect or flaw. It is rimmed in ashen metal and stone, it speaks of ancient bygone ages, something cyclopean to its size and shape.
Opposite the mirror a basin to be filled with water, above that basin directly opposite the mirror a curving pole, topped now with a strange device, a mirror and candle holder angeled to reflect both on the water and the mirror.
The Guardians managed to open the Portal, which shows a world floating in an impossible void