The radio and radar station set up at Aird Uig, Gallan Head, 60 years ago was part of Nato's early warning system against Soviet submarines and aircraft.
Gallan Head Community Trust bought the site from the Ministry of Defence with help of grant funding.
It is working on turning parts of the site into a space observatory.
A marine research centre is also planned at what is to be called The Cetus Observatory.
The trust said: "Cetus will be a ground-breaking, multi-purpose space for observing the dark skies, changeable weather, listening to and spotting whales and getting absorbed in every aspect of nature and science.
"The observatory will hold an internet operated robotic telescope, a small radio telescope, a small radar, a solar telescope, a planetarium, a space exhibition, giant wide field binoculars for viewing cetaceans and birdlife, nature webcams, a cafÃ©, educational facilities, and a small shop.
It added: "Outside the centre there will be a circular path around the headland, in some places leading to observation shelters, excellent for daytime marine life spotting walks or night-time star gazing."
A ceilidh and a torchlight procession are to be held on Saturday to mark a year since a community buyout of a Cold War surveillance station on Lewis.