The construction time of the pavilion Temple in Monrepo is unknown. From Ludwig Nikolai's letters to his son Paul, it follows that in 1798, the projects of two "temples" for Monrepo were handled by Giuseppe Martinelli, but he based them on the work of Tom de Thomon. Alongside the construction of the building, landscaping work was carried out: the land was cleared of boulders, trees were thinned, and a hedge was planted. Two large fir trees were left next to the new building. One of them has survived to this day.

On the peninsula now called Neptune Peninsula, the land was cleared of stones and a terrace was built on the side of Ludwigstein Island. The natural vegetation on the site was thinned, but some old fir trees were preserved.

Such buildings, styled after antiquity, were very common in park landscapes at the end of the 18th century. Often pavilions were made of stone, but wooden structures called temples were also found.

In the poem "The Monrepo Estate in Finland" (1804), Ludwig Nikolai mentions a "Greek-style open temple" under construction, next to which stand two old fir trees. Presumably, at the time the poem was being written, the construction was not yet completed.

Inside the building was a sculptural composition depicting the goddess Pietas holding an infant, symbolizing the fulfillment of duty to the gods. For this reason, the building was originally called the Temple of Piety. Nearby, on the veranda, a sculpture of Neptune was installed on a pedestal decorated with a school of dolphins.

Both Neptune and the pedestal with dolphins were acquired by Nikolai as part of a large group of antique sculptures he purchased from the architect Vincenzo Brenna. Later, the sculptural image of Neptune or Jupiter was moved inside the Temple along with the pedestal, and the pavilion began to be called the Temple of Neptune.

Several research works have suggested that in the 1830s, the design or repair of the Temple pavilion in Monrepo was undertaken by A.I. Stackenschneider, but these claims are unconfirmed.

On the site where the pavilion stood, shore reinforcement works were carried out, a fir hedge was planted, and on two sides of the Temple of Neptune, two pines were planted, one of which has survived to the present day.

The building survived until 1948 but was later dismantled due to dilapidation. In 1999, with the participation of the public organization “Pro Monrepos,” the temple was restored. Unfortunately, the structure completely burned down in June 2011 under unknown circumstances.

In 2018, it was restored again.

Sources:

https://peterburg.center/maps/gosudarstvennyy-istoriko-arhitekturnyy-i-prirodnyy-muzey-zapovednik-park-monrepo.html

https://www.spb-guide.ru/page_20244.htm

https://wikimapia.org/5184960/ru/%D0%A5%D1%80%D0%B0%D0%BC-%D0%9D%D0%B5%D0%BF%D1%82%D1%83%D0%BD%D0%B0

After acquiring the Monrepo estate in 1788, major work began on rearranging the park, during which in the 1790s three attempts were made to install a Tuscan column, but as researchers believe, the result did not satisfy the estate owner, who envisioned the future monument on a "hill leveled and sown with clover on three sides." By his order, a flat hill was built on a small island, on which a marble column was erected in 1804.

Originally designed as a monument to Paul I, the column was ultimately dedicated to both him and his son Alexander I. On the now-lost plaque located on the pedestal, there was an inscription in Latin: "Caesar nobis haec otia fecit" ("Caesar gave us this peace") — a paraphrase by A. L. Nikolai of Virgil's expression: "Deus nobis haec otia fecit: namque erit ille mihi semper Deus" ("God has given us this peace: for he will always be my God"). The meaning of the inscription is explained in Nikolai's poem "The Monrepo Estate in Finland. 1804":

…A short grateful inscription,

Which you can read on the pedestal of the column

Made of Finnish marble. It

Says: "Caesar has granted us peace."

The words are meant for both:

You, Paul, rewarded me for long service

Like a tsar, gave me everything to decorate here.

Freeing my neck from the yoke,

Then Alexander,

Your gentle son,

Allowed me to own the estate personally,

To peacefully end the evening of life…

Indeed, upon ascending the throne, Paul I showered his former mentor with favors: awarded him an order, gifted land holdings, and granted a baronial title. In turn, Alexander I fulfilled Nikolai's earnest request to retire, and by his decision freed the Monrepo estate from burdensome taxation (referred to in the poem as the "yoke") and transferred it from temporary to hereditary ownership by the baron.

Despite the lost plaque, the oldest monument in Vyborg, unlike many others (such as the monument to Väinämöinen, the sculpture of Narcissus, the monument to Mikael Agricola, the monument to the White Finns, the Independence monument, the monument to Peter I, the monument to Torgils Knutsson, and others), successfully survived the period of the Soviet-Finnish wars (1939–1944).

According to preserved documents, the commemorative sign was relocated several times, as earthworks and landscaping were carried out on the island. The current monument is made of gray-green marble and stands on a high pedestal.

Sources:

https://peterburg.center/maps/gosudarstvennyy-istoriko-arhitekturnyy-i-prirodnyy-muzey-zapovednik-park-monrepo.html

https://ru.wikipedia.org/wiki/Column_of_the_Two_Emperors