Marksburg
Every other major castle in this guide is a ruin, rebuilt, or both. Marksburg is the exception: built in the early 12th century on a steep conical hill above Braubach, it was never seriously besieged, never blown up by the French, and never demolished for stone. What you walk through today is close to what a working Rhine fortress actually looked like in daily use — not a 19th-century Romantic-era reconstruction dressed up to look medieval.
Why it survived when nothing else nearby did
Marksburg's hill is steep enough on every side that a siege army had no practical approach — attackers would have had to climb under fire on a slope with almost no cover. That made it not worth the cost of taking, so it changed hands mostly through inheritance and treaty rather than conquest. When French revolutionary forces swept the Rhine in the 1790s and demolished most of the valley's castles as a matter of policy, Marksburg was used as a prison and later a disabled-veterans' home instead — a mundane administrative use that, paradoxically, is exactly what kept its walls standing.
What's inside
The castle is accessible only by guided tour, run on a fixed schedule rather than open self-guided wandering — a deliberate choice that keeps the fragile original stonework from becoming a free-for-all. The tour covers the Gothic hall, the battery gallery with its original cannon, a herb garden still planted with the same medicinal and kitchen plants a medieval household would have grown, a knight's hall, and a torture chamber that's more matter-of-fact museum display than horror-show theatrics. The kitchen retains its original open hearth and soot-blackened stone, one of the best-preserved medieval castle kitchens on the Rhine.
Getting up there
Marksburg sits above the town of Braubach on the river's right (east) bank, roughly 12 km south of Koblenz. There's no cable car or shuttle — it's a genuine uphill walk of about 15–20 minutes from the town centre on a paved path, steep enough that comfortable shoes matter. Drivers can park in Braubach and walk up; the castle isn't reachable by car itself.
How it compares to Rheinfels
If you only have time for one castle interior, the choice comes down to what you want to see: Marksburg for an intact, furnished medieval fortress with a fixed guided tour, or Rheinfels for a sprawling ruin with tunnels and ramparts you're free to explore at your own pace. They're genuinely different experiences, not a better-and-worse pair — see the Rheinfels guide for the comparison in full.