According to the legend, in the early 1400s a man named Christian Rosenkreuz (German for Rose-Cross) took a pilgrimage to the Middle East and learned among Turkish, Arab, and Persian sages and Sufi or Zoroastrian masters lost and esoteric wisdom. He then supposedly returned and founded the "Fraternity of the Rose Cross" and had a secret temple, the Sanctus Spiritus, or "The House of the Holy Spirit" built.
No such man, or temple, ever existed and the modern day Rosicrucians say as much. The first documents regarding Rosenkreuz, and Rosicrucianism surfaced in Germany a hundred years after Christian Rosenkreuz is supposed to have lived. Showing up in the early 1600s as anonymous manifestos citing a "most laudable Order" the Rosicrucians, consisting of a group of mystic-philosopher-doctors promoting a "Universal Reformation of Mankind." Rosenkreuz himself only shows up in the third of these documents, and may have been a stand in for a actual person, possibly Francis Bacon.
The documents themselves were encouraging of religious reform, mysticism, and alchemy, but may have been intended as no more than satire, or even hoax. Johann Valentin Andreae claimed later in life to have written the third of the documents and called it a "Ludibrium," a trivial game or farce. Whether intended as satire, hoax, joke, or as a reform tract, it was a massive success. The idea of a secret society of alchemists with esoteric ancient knowledge from the East, caught fire in Europe.
Like the current Priory of Sion myth (another ludibrium made up in the 1950s, which has led to the Da Vinci Code and popular conspiracy theories) the Rosicrucians were too good a story to pass up. Since the supposed society was secret, actions could be taken anonymously by whomever wanted in on the joke. In Paris in 1622 two posters showed up on the walls reading "We, the Deputies of the Higher College of the Rose-Croix, do make our stay, visibly and invisibly, in this city" and "The thoughts attached to the real desire of the seeker will lead us to him and him to us."
In a example of life imitating art, the myth gave rise to real organizations. Inspired by the idea of a secret society of learned men, astronomers such as Johannes Kepler, Georg Joachim Rheticus, John Dee and Tycho Brahe formed an actual society, known as the Invisible College, to acquire knowledge through experimental investigation. It would eventually become the Royal Society.
It would not be until the mid 1800s that what we think of as the Rosicrucians would form. Starting as groups intertwined with Masons -- another secret society with fictional ancient ties to the East-- the Fraternitas Rosae Crucis was formed in in 1858. (In the 1900s Christian-Rosicrucian groups separate from the Masons began to emerge, such as the Order of the Temple of the Rosy Cross, associated not with the masons but with the 1900s occult group, the Theosophical Society.)
Begun in 1858 by doctor, occultist, and writer Paschal Beverly Randolph, the Fraternitas Rosae Crucis is the oldest of the modern Rosicrucian movements and is considered the main Rosicrucian organization today. A friend of Abraham Lincoln and descendant of William Randolph, Paschal Beverly Randolph was of mixed race, a major proponent of reform and birth control, and (though generally glossed over by the Rosicrucians today) was a practitioner of "sex magic" or mystical rituals involving sex.
It is this order, the Fraternitas Rosae Crucis, (revived in 1920 by Reuben Swinburne Clymer) that settled in Pennsylvania, and today owns land in Bucks County on which three Rosicrucian pyramids sit. The headquarters of the Fraternitas Rosae Crucis, besides the three temples, it includes a number of normal buildings and "The Beverly Hall," a large stone building named after the fraternities founder Paschel Beverly Randolph.
Surrounded by "No Trespassing" signs, the pyramids are aligned smallest to largest and covered in Rosicrucian symbolism inside and out, including images of a winged world crowned by a skull and crossbones, and the infamous pyramid with floating eye -- which the US used first in the Great Seal and which the Masons and Rosicrucians lifted for their own symbolic purposes, but which inspires no end of conspiracy theories. Also on the pyramids are commemorations of Masonic groups and leadership, such as the Supreme Councils of nine, seven, and three, and the Supreme Grand Master, Member Sublime Third, and Hierophant. Among those cited are Benjamin Franklin who was a prominent member of the Masons (back when the Mason's were a science-minded reform society) as well as a supposed member of the Paris Rosicrucian lodge.
Today the Rosicrucians, like the Masons, wield little power and are not much more than supper clubs and networking opportunities, with an increasingly aged membership. They do however continue to practice the secret Masonic and Rosicrucian rituals -- based largely on what 1600 and 1700s nobles imagined ancient Eastern rituals might be like -- and according to locals, during the summer solstice, the Fraternitas Rosae Crucis perform a solstice ritual in ceremonial robes, standing in circles around the pyramids and chanting loudly.
The Rosicrucian pyramids can be seen from the road, but they are on private property and if caught snooping you will be chased off and likely prosecuted for trespassing. It is possible however, that if you contact the group they may be more than happy to arrange a tour of the grounds.