Alwyn is one of The Rebellion’s most important provider of supplies, and was built on an ancient First Ones' communication device which is still working.
When Entrapta disrupted Etheria by hacking the Black Garnet, it caused the device to be reactivated and project old holographic recordings of the First Ones. Believing the recordings to be ghosts, the farmers of Alwyn got scared and fled the village, causing The Rebellion to lose contact with the outpost.
Adora, Glimmer, Bow and Swift Wind were then sent to investigate the loss of communication with Alwyn. There, they meet the several ghostly apparitions of the recordings. Despite being scared at first, Bow eventually managed to identify them as holographic recordings of the First Ones, which were produced by the ancient communication device. Adora then shuts off the device, ending the holograms; but this also activates the transmission of a message (which is later revealed to concern Mara (the previous She-Ra), the name Serenia, and a portal) from a lost station of the First Ones.