According to the mainstream version of events, in January 1933 (i.e. even before Hitler became the head of the German government), Himmler accompanied Adolf Hitler during the election campaign in Lippe district (a neighboring district to Paderborn) and had developed the idea to use a castle "in the heartland of Hermann der Cherusker" to establish the SS Leadership School.
Hermann der Cherusker (better known as Arminius) was a chieftain of the Germanic Cherusci tribe (and a former Roman lieutenant-general). In 9 AD he famously led an allied coalition of Germanic tribes to a decisive victory against three Roman legions in the Battle of the Teutoburg Forest thus ensuring independence of Magna Germania from the Roman Empire.
Incidentally, the Teutoburg Forest extends from western surroundings of Osnabr;ck in the northwest to the eastern surroundings of Paderborn in the south.
During the Unification of Germany in the 19th century, Arminius was hailed by nationalists as a symbol of German unity and freedom, and was celebrated as a national hero.
Initially, Himmler wanted to buy or lease another castle - Burg Schwalenberg – a 13th century castle on the hill above the city of Schieder-Schwalenberg is a town in the Lippe district.
But negotiations failed in the fall of 1933, so he followed the advice of Adolf von Oeynhausen – NSDAP and SS Leader in the neighboring city of Minden – who recommended the Wewelsburg castle.
According to an alternative version, von Oeynhausen (or the owners of Burg Schwalenberg that refused to sell or lease the castle to the SS) had nothing to do with Himmler’s decision to lease the Wewelsburg castle. The latter was recommended to Himmler by one Karl Maria Wiligut.
Like Adolf Hitler, Karl Maria Wiligut was an Austrian, a baptized Roman Catholic and a decorated war hero. Unlike Adolf Hitler, he spent not four, but forty years in military service to the Austrian-Hungarian Empire. At the beginning of the Great War he was a mere lieutenant; by the end of the war he was promoted to full colonel. He retired from the military service on 1 January 1919 with an impeccable record.
What happened later is a bit of a mystery. A year after his discharge from the German Army he got interested in (and most likely involved with) Ordo Novi Templi (the Order of New Templars) established twenty years earlier by none other than J;rg Lanz von Liebenfels.
The latter used this organization to disseminate his ideas, which he first described as "Theozoologie" or "Ario-Christianity" and from 1915 as "Ariosophy". The order associated Christian piety with modern concepts of racial studies and eugenics. Apparently, these ideas struck a chord with a retired colonel and he began to develop esoteric ideas of his own.
And then the tragedy struck. In 1924, a twin brother of one of the girls died as an infant. It was a devastating loss for Wiligut who was desperate for a male heir to which he could pass on his "secret knowledge" accumulated over the years of occult studies.
He apparently suffered a severe nervous breakdown which resulted (probably) in some mental health problems and (definitely) in a regular physical abuse of his wife. By the end of the year she had enough and on 29 November 1924 had him committed to the local mental hospital where he was held (against his will, of course) for a couple of years.
Wiligut's medical records reflected violence at home, including threats to kill his wife, grandiose projects, eccentric behavior and occult interests (which apparently were considered by psychiatrists as a mental illness).
He was promptly diagnosed with schizophrenia and megalomania and was declared legally incompetent by a Salzburg court. He was then committed to a Salzburg mental asylum, where he remained until 1927.
Whether it was, indeed, the case or some bribes were involved, remains a mystery. In 1932, he abandoned his wife and family, and (like Hitler twenty years earlier) emigrated from Austria to Germany, finding a new home in Munich.
There he apparently joined the local branch of Nordische Gesellschaft ("Nordic Society") – an obscure association founded in 1921, with the objective of strengthening German-Scandinavian cultural and political cooperation. By that time it was firmly under Nazi control (more specifically, under the control of chief Nazi ideologue Alfred Rosenberg).
In September of 1933, at a conference of the Nordic Society, Karl Maria Wiligut met Heinrich Himmler. What was discussed during that fateful meeting, is not known (and probably will never been known) but it was important enough for the SS Reichsfuhrer to triggered the meteoric rise of the retired colonel in the SS.
Being a fierce champion of eugenics and of racial hygiene, Himmler took mental health issues very seriously. Consequently, it is simply inconceivable that he did not order a thorough investigation of Willigut’s problems in this department (he had plenty of resources to do it even in then-independent Austria).
Given what happened later, this investigation obviously revealed that Wiligut had no mental health problems whatsoever and that bribes, indeed, were involved.
Wiligut was immediately inducted into the SS (under the pseudonym "Karl Maria Weisthor") to head a Department for Pre- and Early History which was created for him within the SS Race and Settlement Main Office (RuSHA). In April 1934 he was promoted to the SS equivalent of his old colonel rank (Standartenf;hrer), and six months later made head of Section VIII (Archives) for RuSHA.
In November 1934 a promotion followed to the rank of Oberf;hrer (“senior colonel” – it has no Army equivalent), and then in the spring of 1935 Wiligut was transferred to Berlin to serve on Himmler's personal staff under Karl Wolff. He was promoted to the rank of Brigadef;hrer (equivalent to one-star general) in September 1936.
Given the fact that it was Wiligut who developed the overall plans to transform the Wewelsburg castle into the “center of the world” and that it was his friend and disciple SS Obersturmbannfuhrer Manfred von Knobelsdorff who became the first SS commandant of the castle, the alternative version of events is far more likely to be true and correct.
So, following the advice of Karl Maria Willigut, on November 3rd, 1933, Heinrich Himmler visited the castle. He liked what he saw (and felt) so in the first half of 1934, a 100-year lease was agreed for a purely symbolic annual rent of one Reichsmark (plus the promise to finance all restoration work, of course).
Now Heinrich Himmler and the SS could begin implementing whatever they planned for the Wewelsburg castle.