A mild elevation to the north of Vimperk castle has a small fortress on its top, a kind of miniature castle. It is an artillery bastion called Haselburg, an outpost which was built to compensate for the unfortunate position of the castle itself. At the time when artillery was gaining in importance, the elevation, higher than the castle in altitude, would have constituted an ideal firing position for the cannons of the besieger. The bastion originated around 1479, when the fortifications of the castle and the town were integrated into a single defensive system for Vimperk. The bastion was originally surrounded by a lined moat and protected by two circles of ramparts, of which the outer one is now largely gone. The whole horseshoe-shaped complex has a massive outer wall, which is strongest in its most exposed arched section. A mighty round tower is built into the wall on the entrance side, with a cross vault in its interior. The ground floor originally had two more storeys above it, the top one used as a residence. The entrance gate still bears a stone slab with the Kaplířs of Sulevice’s coat of arms and the date 1479.
In 1729 an order was issued to pull the old Haselburg bastion down as it could not be further preserved and had lost its importance. The material gained from the demolition was to be used to repair the castle. Fortunately, the order was not carried out, saving the only outlying artillery bastion in Bohemia which has been preserved to this day.
Today, Haselburg is a poetic mediaeval structure surrounded by a picturesque array of houses. As it is privately owned, it is closed to the public.