Camp Hi-Ho in Simpsonville was engulfed in flames late Friday night -- with their main barn on the property being reduced to rubble and ashes. The barn served as a sanctuary for a number of activities and attractions the Lawrences put on for kids each summer ... not to mention living and workspaces they themselves used.

TMZ has obtained an email that J. Law's brother -- owner and director of Camp Hi-Ho, Blaine Lawrence -- sent to parents of campers past ... and it details exactly what was destroyed in the fire, which was a lot more than just a mere barn.

He writes that the barn housed an office space he used, plus a separate apartment the Lawrences often utilized personally. Not only that, but it encompassed the stalls for their horses, the indoor riding area for kids, an indoor rock wall they had, a native wildlife display center, an arts and crafts pavilion, a garage loaded with farm equipment a new nurse station ... and more. All of that is gone.

Thankfully, Blaine says there's still a lot that wasn't taken in the fire -- including their outdoor sports court, their tree fort space, their pet barn, the lake area, the archery range, the animal pastures and outdoor horse-riding trails, a hen house and other campsites.

While Blaine is thankful to still have those parts of the camp intact -- on top of not losing a single animal or human life -- he notes that he and the family are still devastated. On that note, he vows to rebuild and open again for summer 2021.

Blaine also asks for community donations via a fundraiser or a 501(c)(3), and for families to sign up and come back to camp, noting he'll do whatever is in his power to make the place like new. Authorities are investigating the cause of the fire.