Marienburg castle, built by the Livonian order, is in Aluksne district. From the castle Marienburg almost nothing left. However, there is a legend clay pots filled to the brim with gold, or stored in the cellars of the castle, or in the local vicinity. The ruins of the Marienburg castle located on the island, in the southern part of lake Aluksne, and form an irregular hexagon. The island is still called Marias. Castle called Marienburg, because until 1917 the town of alūksne was called Marienburg in honor of the virgin Mary.

From the castle Marienburg on the Peninsula Casetas passed the bridge length of 120 meters. Part of the bridge, if necessary, stand. The length of the castle was 200 meters long and 100 meters. The castle was surrounded by a fortified wall, the width of which was about 2 meters and a height of 10 meters. The castle stood 8 towers, which were located on the perimeter walls. Each tower had a diameter of 10-14 meters.

Marienburg castle was founded in 1341 by ordermaster the Livonian order Burchard Kalevaram. The fortress was built to protect the city from attacks of the Russian troops. The castle was regularly subjected to assaults by Russians, poles and Swedes.

In 1658 the town of Marienburg was captured by the Russian troops led by Athanasius Masakini, and given into the ownership of Russia. However, after 4 years, Karaiskou the contract, he leaves Sweden. In 1702 the castle again besieged by Russian troops under the command of count Sheremetev. The count orders to earthworks for artillery devices. These ramparts have been preserved to our days. Many do not even suggest that they are part of the siege works, and not of the natural landscape.

It is interesting that folk legend holds that the mountain Russian soldiers trained in their own caps. But why and for what purpose, history is silent. However, there is a version that Sheremetev, guided by the order of Peter the great, was looking for here buried near the castle of Templar treasure. It is prohibited to use a more serious means for embankments device. This was done to ensure that people had no opportunity to hide the findings. Therefore poured a mountain and is called the temple kalns. In translation from Latvian it means "Temple mount", but the name specifically refers to the knights Templar. But in the annals of the smaller mountain that existed here before the arrival of the crusaders, contained Latgalian wooden fortress. According to another version it is known that the mountain was so called from 1807, when there was erected a monument – a Temple of Glory to the soldiers (Russians and Swedes) who fought for Marienburg.

In the XV century, the castle walls were thickened in some places up to two meters, especially under Windows. It is believed that in these places the Templars and hidden treasures. They say that in 1702 was produced by the explosion of the castle, allowed to reach the gold, which Peter the great built the city of St. Petersburg.

The castle was blown up after a two-week siege. Swedish troops surrendered and left the castle with weapons and banners. But 2 Swedish officer destroyed the fortifications, blew them up, so they have not got to Russian. Since then, alūksne castle was never rebuilt. Currently in the ruins of the castle created an open platform.