Fort I in Kaliningrad, Military fortress in Bol'shoe Isakovo, Russia.

Fort I, also known as Stein, is a red-brick fortress built in 1875–1879 on the outskirts of Kaliningrad, in present-day Bol'shoe Isakovo. Its wide facade has a central arched gateway topped by a carved crest, rows of recessed windows on both wings, and a sloped earth-and-grass embankment covering the top. A water moat once reached a depth of two metres, with a bridge at the rear connecting the fort to the surrounding land.

The fortress was built in the late 1800s as part of a major upgrade to the city's defenses following advances in military technology. Its creation reflected strategic concerns that arose from conflicts and political shifts happening across Europe at that time.

This fortress served as a crucial military hub that shaped how the city was defended and organized during the 1800s. Walking through the exterior, visitors can still see where soldiers lived and worked, revealing how military life was structured here.

Visits are only possible with a guide, since restoration work continues after the fort reopened in July 2022. The brick facade with its arched gateway and the earth-covered roof are best seen on foot; the paved ramp up to the archway is cracked, so watch your step.

The fortress follows a geometric design with repeated regular patterns that shape how the structure is laid out. This systematic approach to its design was common in military architecture of that era and helped make defenses more efficient.