The former mansion of Nikolaev in Zelenogorsk is considered one of the main attractions of the city of Terijoki and has gained international fame. The main building and outbuildings were constructed at the turn of the 19th and 20th centuries. During World War I, the estate was acquired by the honorary citizen of the city, Ivan Ivanovich Nikolaev, under whose name the house entered history. The fate of Nikolaev, the most famous owner of the mansion, remains unknown; he disappeared during the years of revolutions and turmoil, like many others of that time.

In 1917, the house passed to Ivan Martynovich Lassman, and in 1927 it was purchased by pharmacist Uuno Hagber, who became the last private owner of the mansion. Later, the building came under the control of Finnish military: first, it housed the border guard headquarters, and then the officer's assembly of the 1st Jaeger Battalion of the Finnish army.

After the USSR attacked Finland in 1939, the Finnish army was forced to retreat, and Terijoki was occupied by Soviet troops. Soon after, a puppet government called the 'Finnish Democratic Republic' was established here, led by Otto Ville Kuusinen. A lot of time has passed since then; Finland honorably concluded the war, not allowing itself to be defeated, and the locals nicknamed this house 'Mannerheim's Dacha,' after the true ruler of Finland during those years. This humorous name stuck, and the house is still referred to as such by the residents of Zelenogorsk.

Today, the building has long been abandoned and is in a deplorable state: windows are partially shattered, partially boarded up, the roof is leaking, and the doors are broken. Thus, we risk losing not just an old house, but a monument to an entire era, whose bloody mistakes and crimes must never be repeated.