Hirosaki Castle is a landmark in Forza Horizon 6 modeled after the real Hirosaki Castle in Aomori, Japan, and it plays a role in the game's Classy Castle photo challenge tied to the winter portion of the Italian Exotics series, according to Polygon.
On the castle's location, the two sources give slightly different descriptions. Polygon places it on the eastern side of the Takashiro region, on a rectangular plot of land surrounded by water just north of a lake, with the castle itself sitting in the southeastern corner of that raised plot. PC Gamer instead describes it as being in the northeast of the Takashiro region, not far from the eastern edge of the map, and notes it's a marked, named tourist location on the in-game map.
PC Gamer adds that the Hirosaki Castle speed trap event sits at the center of the area and will place players right at the castle's gates, and that the Hirosaki Scramble dirt race is also nearby.
To complete the Classy Castle challenge, players need to photograph a classic sports car at the castle. Both sources point to the 1971 Nissan Skyline 2000GT-R Barn Find as an easy option since it's free to obtain, and players can check their garage by filtering for 'Classic Sports Car.' PC Gamer also lists the Mazda RX-3 and Chevrolet Corvette as examples of qualifying cars.
Completing the challenge rewards a White Suit clothing item, according to both sources. PC Gamer adds that it also grants two Festival Playlist points, which count toward that week's reward cars, the 1982 Lancia 037 Stradale and 2020 Ferrari Roma, as well as the Series' milestone rewards, the 2024 Lamborghini Temerario and 2022 Ferrari 296 GTB. PC Gamer also notes that a cold front has covered the map in snow, adding difficulty to locating the castle and other landmarks this week.