Burgruine Marstetten, Medieval castle ruin in Aitrach, Germany.

Burgruine Marstetten stands on the Burghalde at 657.8 m above sea level in the Zeiler Schotterfeld on the edge of the Iller valley. The site is split by the L314 road: Alt-Marstetten lies south of the road, the newer section north of it. The surviving walls are of rough stone rubble with scattered red bricks, pierced by two small arched recesses and a larger arched opening at the right edge; vegetation grows along the broken top.

The fortress began in the 11th century under the Ursin-Ronsberg margraves who controlled the surrounding region. Swedish military forces damaged it heavily during the 1600s conflict, after which it was abandoned and left to decay.

The name Marstetten comes from the site's role as a boundary marker between the Illergau and Nibelgau and between the territories of Kempten Abbey and Ottobeuren Monastery, a function recorded around 838. The county of Marstetten held high jurisdiction, with its court seated in Memmingen. The ruin belongs today to the House of Waldburg-Zeil.

The ruins are reached by foot from a nearby parking area on the road toward Bad Wurzach. The walk uphill takes about 10 to 15 minutes and is moderately steep, so sturdy shoes are helpful.

The ruin straddles the L314 road between Bad Wurzach and Aitrach: the older Alt-Marstetten lies south of the road, the newer section north of it. The name itself records a boundary function from around 838, when the site separated the Illergau from the Nibelgau and the Kempten abbey lands from those of Ottobeuren.