The €7-million ($10-million) exhibition, dubbed the world's first dedicated entirely to the dreaded Schutzstaffel, charts its growth from Hitler's elite guard to a band of more than a million men who committed unspeakable crimes across Europe.
Among previously unseen items is SS leader Heinrich Himmler's diary, showing visits to the castle planned in his spidery script, as well as uniforms and devices used to test whether officers were "Aryan" enough.
Also included with the 1,000 pieces on show are two Totenkopf rings, silver bands engraved with Himmler's signature given to senior officers, with a swastika and the Sig Rune, the instantly recognisable SS symbol.
Wewelsburg Castle, an imposing 17th century triangular edifice on a hilltop south of Hannover in central Germany, itself played a pivotal role in SS history.
Himmler took out a 100-year lease on the castle in 1934, just after Hitler's Nazi party came to power, and intended to transform it into a training school for elite SS officers.
Later he developed more ambitious plans to take over the surrounding village and build an SS capital city with the castle at "the centre of the new world" after the "final victory."
Wewelsburg hosted meetings of top SS generals, including a key rendezvous in June 1941 on the eve of the invasion of Russia where Himmler told the assembled Nazis the goal was "to kill 30 million Slavs."
Himmler ordered bizarre renovations to the castle, creating a spooky circular crypt with a gas pipe in the floor for an eternal flame, a Nazi swastika in the ceiling and 12 pedestals at even intervals around the walls.
This room has given rise to a host of myths about Wewelsburg, that it was conceived as "Himmler's Camelot", designed to hold meetings with his 12 top generals as King Arthur once convened the Knights of the Round Table.
Moritz Pfeiffer, a 27-year-old historian who helped design the permanent exhibition, said torch-bearing SS guards or statues probably stood on the pedestals. But he scotched the myth that Himmler conducted bizarre pagan rituals in the echoing crypt.
"That can't be scientifically proven," he said. "We know the number 12 crops up time and again in the castle, but we can't say exactly what that means."
Directly above the crypt is the "Hall of the Supreme SS Leaders," another circular room supported by 12 stone pillars with a mysterious occult symbol known as the "schwarze Sonne" or "black sun" set in the floor.
The symbol, a dark circle with 12 crooked "spokes" making up the "sun," has baffled historians and fascinated neo-Nazis who have adopted it as an alternative sign to the swastika, which is banned in Germany.
Indeed, the castle has become a magnet for neo-Nazis and authorities are aware the new museum could attract unwanted attention from the far-right.
"We had people coming to the castle and performing the Hitler salute. You can only deflect this way of thinking if you show where it leads," Heinz Koehler, the deputy head of the local administration, told AFP. "We reserve the right to throw people out."
Among those expected to attend the opening was 104-year-old Leopold Engleitner, an Austrian survivor of the concentration camp near the castle where 3,900 people were held. One third of the inmates died.
The museum commemorates victims of the camp, including Günter Ransenberg, a 15-year-old Jewish boy who accidentally hit the daughter of an SS officer during a friendly snowball fight.
He was hanged for "racial crimes."