Trail of the unexpected: Göta Canal

It takes less than four hours by train to travel between Gothenburg and Stockholm, Sweden's largest cities. But if you're not in a hurry, you might prefer to spread the journey over four days aboard the three-deck M/S Diana, built in 1931 – and let the "Coast to Coast" pleasure cruise take you back to a bygone era.

Crew-member Viktor left my bags in my cabin, whispering, "There isn't a radio, the internet or even a television set on board." My cabin was small, but magical – all gleaming mahogany panelling and polished brass fittings. Unpacking, I saw a series of timber houses behind swathes of birch trees drift past my window: we'd set off already, albeit at a sedate four knots.

Diana's route would take us right across Sweden, mostly along the spectacular Göta Canal, dreamt up in 1810 by Baltzar von Platen – a naval officer and politician who believed it would boost trade and improve his country's defence system.

Twenty years later, with the help of the Scottish engineer Thomas Telford and 58,000 workers, the 190km link between the coasts of Scandinavia's largest nation was completed.

The crisp warm rays of a spring sun beamed down on me and the other passengers – 40 or so affable Americans, Australians and Scandinavians – as we came across our first lock after Gothenburg, at Lilla Edet. I found a vantage point and watched as our crew flung ropes onto the lock walls to moor Diana to bollards. Ten minutes later she'd risen five metres. The gates opened and we were on our way again.

An early landmark was the Baroque Lackö Slott. Built in 1298, the castle stands on a peninsula that juts into Lake Vanern, its soft pink walls and dome-topped turrets casting a dreamy reflection over the water. It's a fairytale scene which Hans Christian Anderson would undoubtedly have noticed when he made this journey around 170 years ago on the Juno, one of two older passenger liners constructed by the same company as the Diana.

Meals onboard ship were something to savour. Food is sourced locally where possible (an epic course of sumptuous poached Lake Malaren zander was a highlight), and as we polished off chocolate truffle cake, our craft drifted through canals that were barely wide enough for her.

Every day the itinerary offered excursions from the ship. One was a visit to the impressive mass of yellow limestone that forms Karlsborg Fortress. Yellow it might be, but it is also one of the country's biggest white elephants. It was another brainchild of von Platen. Construction on the fortress's 5km circumference began in 1830 but before it was finished in 1909, the building was already obsolete thanks to military advances.

"This is like no tour you'll have ever been on," said our guide, Per Olof. It was hard to argue with him, as almost straight away a soldier jumped down from one of the battlements and fired a volley towards us. Soon afterwards, as we crept along the dark, dank passages of the castle's inner defences, special effects brought this place to life in the form of hissing rats and the boom of cannon fire.

The next day, we began our three-hour sail through the lock system of Berg, culminating in the magnificent Carl-Johan staircase – the longest series of locks in the canal. From a distance the black-and-white wooden and metal tops of its gates gave the impression that we were negotiating some sort of weird steeplechase as we descended into the gaping yonder of Lake Roxen.

Here we were taken to the first convent in Sweden, Vreta, dating from the 12th century. Nestling in a clearing surrounded by towering spruce and pine, its still-intact ochre-hued church looked like something from a Monet painting.

The nunnery itself has fallen into ruin, its stone walls with their numerous arches and narrow windows crowned with mosses and ferns.

On the penultimate evening, we weaved across lakes draped in mist and marvelled at the medieval town of Söderköping caught in the blush of the Nordic twilight. From there, our journey drew to a close in the waterways of the Swedish capital. Thank goodness that, in 2010, you can still slip back a couple of centuries.

Travel essentials: Göta Canal

Getting there

*The writer flew as a guest of SAS (0906 294 2772; flysas.com ), which flies from Heathrow, Edinburgh and Manchester to Stockholm, with returns from £136. British Airways (0844 493 0787; ba.com ) flies to the Swedish capital from Heathrow; and Norwegian Air Shuttle (00 47 21 49 00 15; norwegian.com ) flies from Gatwick and Edinburgh.

*Gothenburg's main airport, Landvetter, is served by SAS from Heathrow (from £170); and City Airline (0870 220 6835; cityairline.com ) from Manchester and Birmingham. *The city's Save airport is served from Prestwick and Stansted by Ryanair (0871 246 0000; ryanair.com ).

Cruising there

*The Gota Canal Steamship Company (00 46 31 80 63 15; gotacanal.se ) runs four-day "Coast to Coast" cruises between Gothenburg and Stockholm from May to September from SK9,695 (£850) per person, based on two sharing a cabin, full board, with six excursions.

Staying there

*First Hotel G, Gothenburg (00 46 31 63 72 00; firsthotels.com ). Double rooms start at SK1,178 (£102), room only.

*Elite Hotel Marina Tower, Nacka (00 46 85 55 70 200; elite.se ). Doubles start at SK1,105 (£95), room only.

More information

*Stockholm Visitors' Board: 00 46 85 082 85 08; stockholmtown.com

*Gothenburg Tourist Office: 00 46 31 368 42 00; goteborg.com