Festung Hohensalzburg sits on the Festungsberg, a limestone outcrop rising 506 metres above sea level — roughly 150 metres above the old town of Salzburg below. It was begun in 1077 by Archbishop Gebhard von Helfenstein, a Gregorian-reformer prelate who needed a defensible residence during the Investiture Controversy — the great church-versus-state war between the papacy and the Holy Roman Emperor Henry IV. Successive prince-archbishops expanded it for the next five centuries; the version visitors see today was substantially completed under Leonhard von Keutschach around 1500.
It is the largest fully-preserved medieval castle in Central Europe and was never taken by force in over 900 years of standing — though it has been surrendered, notably to Napoleonic forces under General Moreau in 1800, without battle. Successive prince-archbishops invested heavily in walls and outer defences; the only time it actually came under siege, during the German Peasants' War of 1525, the attackers failed to take it. Inside the walls today are the late-Gothic Princes' Chambers (Fürstenzimmer) with their original wooden ceilings and tile stoves, the Magic Theatre and its 16th-century mechanical organ known as the Salzburg Bull, the Marionette Museum, and a working funicular — the Festungsbahn, in operation since 1892 — that connects the fortress to the old town in about a minute.
The fortress is open every day of the year. Tickets are valid six months from the date of purchase, so there is no slot pressure on the booking itself; the pressure is on the funicular, which queues 30 minutes or more between 10am and noon during the July–August peak. Skip-the-line tickets bypass that queue and put you on the next available car.
Most visitors come for the view as much as the history. From the rampart walks the panorama opens across the baroque domes of the old town, the green Mönchsberg cliff, the Salzach winding north, and the limestone Alps to the south — the reason the fortress is Salzburg's defining skyline. Hohensalzburg Fortress tickets cover those terraces plus the Reckturm watchtower and the courtyards, and because admission is open rather than timed, you can linger as long as the light holds rather than racing a slot.