Pavilion on the island, Yelagin Island.

From Ivan Perfilievich Elagin, only one structure remains on the island – the so-called Pavilion on the island or the gazebo "On Four Stone Pillars," as it was called by contemporaries. It is located in the Old English Garden, on the islet of the 3rd South Pond, and looks extremely romantic, especially if you pass by it in a boat. The greenery of the park, the singing of birds, the splash of the oar… and a lonely white gazebo, accessible only by water. It was built by Elagin in the mid-1780s in honor of Vice-Chancellor Count Panin, a close friend and fellow Mason who often visited Elagin. However, it is not certain that the gazebo was originally located on the islet. It became separated from the mainland during the grand earthworks of the 1820s, after several new ponds appeared one after another on the island. Later, the structure was remodeled by Rossi, who introduced elements of late classicism and painted it in the gray color common to the entire ensemble, with architectural details highlighted in white. This building has survived to the present day almost unchanged, giving the park a romantic appearance.

In general, Ivan Perfilievich, apparently, was a romantic soul. Monuments honoring his friends were placed around the park, enlivening the landscape, but K. Rossi was only interested in the gazebo, which he remodeled by adding elements of late classicism and painting it in the gray color common to the entire ensemble, with architectural details highlighted in white.

Judging by old photographs, earlier (at least in the 1960s–1970s) the islet on which the pavilion stands was connected by bridges both to the shore of the pond and to the neighboring islet. Currently (spring 2017), the islet is isolated from the mainland.

Sources:

https://www.citywalls.ru/house28084.html