Like many seekers, I stumbled across the Archive quite by accident, during a meditation. My "zero point" location, my internal place of peace, is actually a beach area in a tropical region, with a dense jungle leading back to some mountains. I was a that interior location and noticed that there were the ruins of a stone city, much like you find in Central and South America with the Inca and Maya. I went to investigate and the only building still intact was this domed temple, overgrown by the jungle. There were two, very large doors at the front that were closed and the building felt of great age. With some effort, I was able to open the doors enough to pass through to the interior, which was a circular room with a sunken, central area that contained a circular, stone table on a column (a stone dais). I walked to the dias and noticed it was engraved with symbols around the edge, much like the DHD of the Stargate series. I began to wonder what it was for, and was running my hands along the symbols--and it reacted. A holographic image appeared above the dais, which appeared to be the inner solar system. Doing the typical "huh" thing, I reached out and touched the 3rd rock from the sun, and it zoomed in on the Earth. After some experimenting, I realized that the symbols were much like a "joystick" that allowed you to navigate through this huge repository of information. Over time, I was able to get specific information--and as I grew in my ability to interface with it, the interface, itself, changed to accommodate. I realized that this was not just some memory bank, but something much more.
After I discovered the Archive, the research of George Hunt Williamson started to make more sense to me. His "little red brick schoolhouse" was his symbolic expression of this Archive, but rather than my Sci-Fi version of a holodeck, he had a room full of books that he could open and read. This was the case for many people accessing the Archive in the late 19th and early 20th century. (There probably exist older tales of the Archive, buried in cultural legend.)
So the first step to accessing the Archive is to locate it. There are two regions that one can explore to find the Archive, which is located in 3D time--not space: meditation or the dreamscape. A deep meditation has many dreamlike qualities because it is overlapping the same, temporal territory: the cosmic sector. The only difference is that it is external to the internal, psychic landscape you perceive--but often has a projection into the internal realm, which takes the symbolic guise of something ancient and spiritual. Giving the religious upbringing of most of humanity, that symbol tends to be a temple, but the temple will be located in a remote, relatively inaccessible place and be closely tied with something that is symbolized as "earthy."
In the Stargate SG-1 episode, "Material Instinct," they did an excellent job of representing this. On a forbidden world of the Locnakoh, there existed a monastery in a fertile valley, away from all other habitation, where the Ancients, the ascended race of the series, left behind a record of their path to ascension--exactly like the Cyclopeans did. (I suspect one of the Stargate writers was familiar with George Hunt Williamson's books...)
So, the first thing one needs to do to locate the Archive, is to go "in" and look for it. In a meditation, find the quiet place, what Doctor Who refers to as "null interfaces" in the Zero Room. Your place of peace, and start searching from there. The symbol you are searching for will be ancient, earthy and primarily natural--but showing some signs of artificial construction (like blocks of stone). There will be some kind of threshold that you will have to cross, which will be symbolic of a challenge. For me, it was the giant doors. In Arthurian tradition of Great Britain, it is often the drawbridge crossing the moat. In modern context, it could be the hanger deck of an abandoned, alien ship. Look for the characteristics, not any specific symbol.
Also of interest, is that of the people that have told me of successful access, there is a path that is in common: you go down a road, path, walkway, then take a left turn towards this threshold--which will either stop you, or trip you up, to try to prevent your crossing it. But once you have crossed, you are not presented with that challenge again. You can go right in.