Altrathen Castle, Medieval castle ruins in Rathen, Germany.

Altrathen Castle is the ruin of a medieval hilltop castle on a rock spur above the right bank of the Elbe in Rathen, Saxon Switzerland. Of the medieval complex, stretches of wall, a vaulted passage and cellars survive, incorporated into a residential building erected in 1902/03. Together with the rock castle Neurathen, about 500 metres to the northwest, it formed a double castle.

Altrathen Castle was first documented in 1289 as a Bohemian fief, and in 1361 a charter of Charles IV named it together with neighbouring Neurathen as two castles. In 1469, after a siege of more than a year, Electoral Saxon troops burned both castles. The industrialist Eduard Seifert bought the ruin in 1888 and had it rebuilt in Neo-Gothic style by 1893.

The names Altrathen and Neurathen are modern coinages; medieval charters speak only of Rathen and rarely distinguish the two castle parts. The higher rock castle Neurathen, despite its name, is considered the older site. Since 2018 Altrathen has been privately owned and is not open to the public.

The castle is privately owned and not open to the public, so it can only be viewed from the outside. It stands on a rock spur above the right bank of the Elbe in Rathen; the rock castle of Neurathen lies about 500 metres to the northwest. Visitors should not expect access to the buildings or the vaulted passage and cellars.

The cellars of the castle were not constructed with stone blocks but carved into the soft sandstone, so the walls still show the marks left by the tools used to hollow them out. These rooms stay noticeably cooler than the outside air even on hot summer days.