Wakamatsu castle, also known as Aizu-Wakamatsu or Tsuruga castle is definitely most famous castle in Fukushima prefecture and may be the most popular castle in Tohoku region.
Unfortunately it is not the original one which date backs to 1384. Wakamatsu castle is called Kurokawa castle until late 16th century. Fierce battle or siege took place in 1868 during Boshin war, the civil war which was fought between Imperial court and the Shogunate.
The castle received a huge damage during the war and eventually was demolished in 1874. Therefore the current castle was rebuilt in 1965.
Wakamatsu castle is not located close to Aizu-Wakamatsu station, therefore you have to take a bus from the station.