Ansitz, ehem. Kastell Festetics, Protected heritage site in Gerersdorf-Sulz, Austria.

Ansitz Kastell Festetics is a two-storey Neoclassical mansion with a hipped roof, not a mansard, built around 1800 in Sulz im Burgenland. Its south front has a five-bay recessed section behind a gallery whose roof rests on six round columns with Doric capitals. A single-storey square-columned gallery extends east to a pavilion with a square lantern and pyramid roof.

Countess Judith Festetics von Tolna built the manor around 1800 as a seigneurial residence, and it soon became the centre of a spa. In 1815 the mineral spring was re-cased, revealing Roman gold coins and a nymph statue; a bath and guesthouse followed in 1816 or 1817. After her death in 1829 the spa changed hands repeatedly and closed in 1850, later serving only mineral-water sales.

The name Kastell is the Hungarian term for a nobleman's residence, used here for a classicist manor rather than a fortified castle. Countess Judith Festetics had it built around 1800 as the seat of the local estate, and after 1815 the mineral spring on the grounds was refitted, with Roman gold coins and a nymph statue found during the work. The estate later served as a spa and bottling site, and since 1980 a castle association has worked to keep the building standing.

The castle is private property and not open to the public; only the park and the 120-metre approach road from the Oberer/Unterer Hauptstraße junction are freely accessible. The Sulzer Straße (L188) runs along the southern edge of the roughly 4.2-hectare grounds, opposite the listed spring house of the Vitaquelle. Slopes to the west and north are wooded and partly steep.

A single-story loggia with square columns leads to a pavilion wing that once served as the entrance to the thermal baths. This architectural connection reveals how the residential area and spa facilities were originally interconnected.