Location
Although the Red Room began exclusively as a location within Agent Cooper's dreams, the inhabitants began appearing in other locations in the town, inciting other elements in the plot, to the point where the Red Room and White/Black Lodge stories became one. After discovering a mysterious map in Owl Cave, it becomes evident to Earle and Cooper — both independently and with different motivations for wanting to visit it — that the entrance to the Black Lodge is located in Ghostwood Forest which surrounds the town of Twin Peaks, at a pool of a substance that smells like scorched engine oil and surrounded by 12 young sycamore trees. This area is known as Glastonbury Grove.
It is said that the key to gain entrance to the Black Lodge is fear —usually an act of brutal murder. This is in contrast to the key to the White Lodge, which is love. Another requirement to enter the Black Lodge through the entrance in Glastonbury Grove is that it may only be entered "...when Jupiter and Saturn meet..." When the above requirements are met and one approaches the pool in Glastonbury Grove, red curtains appear, which the person walks between before the curtains vanish once again.
Read more about this topic: Black And White Lodge