Sunset on the Middle Rhine is a symphony in light, a magical period of shifting shades and deepening shadows when the towering valley comes alive under the conductor's baton of the day's final rays.
As the valley peaks steeple and fold, fading sunlight filters across the river, its cliff-like slopes and the collection of small towns and villages that stud its craggy banks, illuminating the many castles and church spires with a luminescence that appears to glow from within, shifting visibly as the angle drops and finally subsides completely.
This enchanting light show plays out along the Oberes Mittelrheintal, a Unesco-designated World Heritage site encompassing some 42 miles of riverscape that has inspired poets and painters for hundreds of years, all drawn by the profound beauty of the river's immense passage through these slate-based mountains.
It has also inspired a rapidly-growing band of modern-day travellers, seekers not necessarily of light and illumination but an all-round view of the Rhine that has become one of the most compelling and popular trips in the holiday compendium.
River cruising is booming in Europe (indeed, on the Rhine, which is at the top of the river cruising league table) – almost 120,000 British travellers chose a journey on a Continental waterway in 2014, an increase of around 29 per cent since 2012.
It's a dramatic growth curve, and one that is currently being fuelled as much by the latest design of ships as the destinations themselves – a new age of river-borne travelling, if you like.
Take one of Uniworld's latest offerings, the SS Antoinette, for example. Where her fleet-mates were typically highly ornate but relatively modest two-dimensional transports, she is bigger and bolder, featuring additional onboard amenities more befitting of her ocean-going brethren.
At 443ft, she is 82ft longer than her fleet-mates, and carries 154 passengers instead of 132. More importantly, this latest marque of river-cruiser is furnished with a full indoor swimming pool, a cinema, an alternative dining spot atop the ship and a second night-time bar/lounge. There is also a decent-sized spa and arguably the most eye-catching two-deck reception area anywhere on Europe's waterways, topped by a stunning 10ft Baccarat-blue crystal chandelier, originally from New York's historic Tavern on the Green.
Where some of Uniworld's rivals go for sheer size – packing in up to 180 passengers – here things remain on a more human scale, even allowing for the increase in length and amenities.
It all combines to provide the perfect platform for the week-long Castles Along the Rhine voyage, sailing between Amsterdam and Basel and cherry-picking the highlights of Europe's second-longest river, with calls at Cologne, Koblenz, Breisach, Rudesheim, Strasbourg and Boppard.
The Middle Rhine section, with its own son et lumière show each evening, features the delightful Roman town of Boppard and romantic Rudesheim, with its signature cable-car ride to the 19th-century Niederwald Monument and scores of castles and ruins.
Each day, there's a half-day tour around the port or a notable nearby sight, such as Schloss Vollrads, a 14th-century vineyard and castle, and the surprising town of Speyer, with its monumental Romanesque cathedral – the largest of its type in Europe. Alternatively, you can pay a supplement (up to €69) to visit the likes of the well-preserved 12th-century Marksburg Castle or a tour of the Black Forest.
At times it is a slightly hurried process, with the tour guides maintaining their timetable almost to the minute. I would have preferred longer to explore the spectacular French medieval town of Riquewihr and its delightful local wines; and Rudesheim, with its Mechanic Music Cabinet Museum.
Happily, the Antoinette was always a sanctuary of tranquillity, offering refreshing towels and fresh fruit juice on my return, before another memorable dinner in the Restaurant de Versailles.
While seven days felt barely enough to delve beneath the surface of the Rhine's centuries-old history and culture, this was, indeed, an unforgettable snapshot of its riches. And, oh, that fabulous luminous lighting along the deepest part of the valley. If nothing else, I will have to find a new camera to capture its incomparable beauty.
Uniworld cruises are sold in the UK through Titan Travel (0800 988 5867; titantravel.co.uk/uniworld). The seven-night Castles Along the Rhine itinerary costs from £1,699pp including flights, full-board cruise with drinks, transfers, and excursions with English-speaking guides.Reuse content