Glen Castle (Hohenhaupt Castle) is a two-story limestone building without plaster on the slope of Mustamäe in the Nõmme district of Tallinn. It is located in the Glehni Park Forest in the southwestern part of the Nõmme-Mustamäe landscape reserve on the territory of Tallinn University of Technology at Vana-Mustamäe Street, 48.

The castle belonged to the Jälgimäe Mustamäe manor and was built in 1886 according to the personal design of Nikolai von Glehn. The location was chosen very advantageously: on the hillside, with a view of Lake Harku on one side and the towers of Toompea and Tallinn on the other. Glehn was an architect and independently developed the construction plan. The castle features numerous cellars, spiral staircases, towers – all intended to create the image of a medieval knight’s castle. Originally, it was called Hohenhaupt. Later, the residence was renamed Mustamäe Manor. Administratively, the estate belongs to the Keila parish.

The foundation of the castle was built by Glehn himself; later, he also used the labor of prisoners. Every day at 12 o’clock, he signaled the start of noon with a trumpet call from some operas by Richard Wagner. Around the building, a park was laid out, and structures were erected (Palm House 1900–1910; observation tower or observatory 1910; and sculptures "Kalevipoeg" 1908, "Crocodile" 1908).

The interior design was also unusual: the walls on the first floor and the study were covered crosswise with poems and individual words written in different colors. The inscriptions were in several languages: Latin, Greek, French, Russian, and German. Among other things, there was a poem in Estonian.

Nikolai von Glehn was a hardworking man, and one of his hobbies was wood carving. Much in the castle was made by his own hands, for example, tables and chairs decorated with carved human figures.

The fate of the castle is sad: after Glehn left for World War I in 1918, the castle was left without an owner, and over time the residents of Nõmme looted the estate, taking out furniture, doors, and windows. The stones of the castle were used for the construction of other buildings. For a long time, the estate was neglected. The owner himself died in 1923 in Brazil, where he emigrated after the war. Only in 1960, at the initiative of the academic male choir of Tallinn Polytechnic Institute, did restoration of the building begin.

Although attempts were made during the restoration to preserve the castle’s original historical appearance, it was not about restoring the castle in its original form but about reconstruction based on the presumed use of the castle. For example, an additional floor was added to the castle. As a result, the volume of construction work increased, requiring more time and resources than initially planned.

The restored castle was solemnly opened on March 24, 1977, and housed the club building of Tallinn Polytechnic Institute (now the cultural center of Tallinn University of Technology).

Since 1997, Glen Castle has been listed as a national heritage site.

Tallinn’s Glen Castle has repeatedly served as a filming location for feature films. For the first time in the early 1980s, director Igor Maslennikov used it for this purpose. He featured the building in the film "The Adventures of Sherlock Holmes and Dr. Watson: The Hound of the Baskervilles." The castle depicted the exterior of Baskerville Hall from Mortimer’s story (the facade of the residence was filmed elsewhere – at Maryamägi Castle, where the Estonian History Museum is now located).

Here, Hugo’s captive descended from the window along the ivy, and here the body of Sir Charles was found. According to the plot, this is the location of Baskerville Hall.

In the early 1990s, Glen Castle became the residence of Porthos in Georgiy Jungvald-Khilkevich’s film "The Musketeers Twenty Years Later." Here, the hospitable host welcomed his friend D’Artagnan. The film also shows the adjacent park, sculptures, and even the grave of Baron Nikolai von Glehn’s horse.

In 1992, in the film "The Musketeers Twenty Years Later," the castle and its surroundings (the crocodile, etc.) were filmed as Porthos’s residence. A year later, the film "The Mystery of Queen Anne, or The Musketeers Thirty Years Later" was shot in the same location.

In the Soviet feature film "Variant Omega," Glen Castle was shown as the estate of von Schlosser.

Sources:

Places found and photographed by Aleksei Leshkov, alzar007, Gara, altavista, Pinguin with hints from Igor Maslennikov and Arkady Tigai

https://et.wikipedia.org/wiki/Glehni_loss

https://triptoestonia.com/tallinn/dostoprimechatelnosti/zamok-glena/

https://dubikvit.livejournal.com/26094.html