Burg Lahr, Medieval castle ruins in Burglahr, Germany.

Burg Lahr is a small castle ruin above the village of Burglahr in the Altenkirchen district of Rhineland-Palatinate. It stands on a wooded hill about 200 metres above sea level, roughly 40 metres above the Wied river, which now flows south of the site. The nearly 25-metre-high round bergfried dominates the remains, alongside wall fragments, foundations and traces of the moat.

The construction date of Burg Lahr is unknown; it is documented from the 14th century as a Kurköln fief held by the Counts of Isenburg, and is probably older. In 1449 the Archbishop of Cologne pledged it to Count Heinrich of Nassau, and it changed owners several times afterwards. It has been a ruin since the 18th century and was later used as a stone quarry; the surviving walls were secured only in the 20th century.

The name Burglahr combines the castle with the village below, which grew around the Wied crossing. The ruin is not run as a visitor site; a wooden hut built inside it can be rented for celebrations, so gatherings there are private bookings rather than public seasonal festivals.

Access is via woodland paths from Burgstraße, with walking conditions varying by season. A wooden shelter on-site can be rented for group gatherings, making it useful for larger visits or events.

The Wied once flowed around the hill on three sides, but the river has since cut a new bed south of the castle and the village, leaving the ruin about 40 metres above the water. The site later served as a stone quarry before the surviving walls were secured in the 20th century.