At 90km, the Annandale Way is one of the lesser of Scotland's Great Trails. This brevity makes it just right as an unplanned quickie trip of four or five days, through quiet countryside, riverbanks, and the occasional tiny hill. There's just one point where you might get stuck: the notorious Moffat Toffee, at the end of Day Three…

I wanna be the one to walk in the sun

Cos girls just wanna have fun

As I sat in the courtyard of Hoddom Castle, enjoying the coffee and Cyndi Lauper on the piped music, it was one of those rare moments when long-distance walking meets post-punk pop. Ninety kilometres of the Southern Uplands, a long weekend of walking timed for a long weekend of gentle summer weather, a gentle breeze across the oak trees, the distant clank of the combine harvester, meadowsweet and yellow loosestrife dangling above the water. Okay there are other ways of having fun in the sun, like illegal toadstools and disco dancing at Glastonbury Festival. But Cyndi Lauper could also be on about one of Scotland's newer official trails, the Annandale Way.

Most people do the downstream direction – it's a bit easier that way. Especially if you happen to be a salmon. And on average it does seem that most of the users of this trail do it with fins rather than feet. Leaving Hoddom castle, I came to one of those signposts giving the distances to either end: at coffee time on Day 1, I'd achieved 98% of my distance. Ahead, only a couple of dozen more miles would get me to the head of the river. Behind, by contrast, it was 4800 miles to – ahem – the inlets of Greenland. (Reassuringly, the remaining signs and waymarks were human being oriented.)

Despite being in the Southern Uplands, the Annandale Way doesn't have all that much Up

And like the salmon, I was doing it upstream. It was more exciting to be starting at the Solway mudflats looking across at England, and be heading towards the drama of the Devil's Beeftub.

Despite being in the Southern Uplands, the Annandale Way doesn't have all that much Up. The initial 20m ascent is accommodatingly graded over the walk's first 15 km – as it follows the River Annan itself upstream, to and fro across various footbridges, squawked at by ducks and even by a heron.

Hoddom Castle was presented as a bribe to my neighbour Johnnie Maxwell, in recognition of his helpfully doublecrossing the Warden of the English West March. On the hill above he built the Repentance Tower, to puzzle future historians – of Johnnie's many available treacheries and attacks, which one specifically was he repenting of? Ten miles north, I'd pass one of the pele towers from the Border warfare, handsomely restored into a private house with rather too many stairs and a magnificent view. In the meantime, Hoddom Castle finds new use as a contemporary caravan site and coffee stop on the Annandale Way.

After Hoddom, the trail leaves the river on small quiet roads, woodland tracks, and fields with combine harvesters asleep in the corners like monster pussycats. Even the walk's first hill is barely there at all. The 219m Almagill Hill is small but effective. It has long views up and down the wide valley, and a few small knobs of greywacke rock. Between the outcrops are grassy hollows just right for the bivvybag. A slightly rocky little hilltop, under the sunset and then the stars: this could be the Annandale equivalent of Cyndi's all-night disco dancing.

However, the nature of the terrain made a mess of my schedule. The smooth, level paths mean it's only 5 o' clock and far too early to go to bed in a bag. Instead I press on towards a fish supper, protected by the massive windbreak of Lochmaben's town hall, with a view down its wide main street and the backside of Robert the Bruce. The town's Mill Loch has a single swan in the middle under a bloodstained sunset. Then into the darkness along the fairly busy (but at least you can see the headlights coming) B7020.

At which point I'm accosted by a dusk gardener at Kinnel Banks. "Hello there, you walking the Annandale Way?"

Well, with my rather big rucksack, why else trudge the B7020 at 9 o' clock at night?

"So why are you along this road?"

"Well, because this road is the Annandale Way… "

"Ah. You must be using the Walkhighlands GPS track. Or the map."

It's true. Given it's hardly light enough to see and the map says just follow the road, I'm just following the road. But the dusk gardener is a volunteer maintaining the footpath, and they've taken it off the B7020. This is such a good move that I retrack to the edge of Lochmaben, hunt waymarks by torchlight, and settle to sleep in deep grasses beside Kinnel Water.

In the cosy hollow below the embankment, the rustling alder leaves kept me awake for all of 30 seconds. Some time in the night the stars showed for a moment. As the wind died, new soothing sounds took over: the chuckling of the river, and the clanky roar of the A74(M) 3km away. But it's not true what some survey said. A distant motorway doesn't sound at all like a waterfall, unless the waterfall had miscellaneous bits of old iron tipping over every few seconds.

The second day is more of the same, but without any riverside bits. Little lanes, farm tracks, woods and fields and streams. The plantation section over Kinnel Knock has mostly been clear felled, allowing (for the next few years) wide views from a hill that at 227m is 8m bigger even than Almagill was.

As short-distance walks go, the Annandale Way can actually be taken extremely long. I'm on it as part of an extended Carlisle to Glasgow outing, itself part of a book all the way to John o' Groats. The man and his 10-year-old son coming the other way are the same. They've walked here in stages from Spean Bridge. Linking this path with the Clyde Walkway into Glasgow does make one of the natural ways right through the Southern Uplands – while utterly spoiling the point of a short-distance walk.

Moffat is one of the grand sandstone towns, with a double-wide main street. It was the deathplace of John Loudon McAdam, the man ultimately responsible for tarmac roads like the horrid B7020. But as walkers we ignore that and concentrate instead on the famous Moffat Toffee, cunningly constructed in four-cornered stripy lumps. At the town's centre stands a bronze celebration of a local colonist and exploiter of Annandale. This politically unsound fellow was responsible for the clearance of the original population and lifestyle. He has yet to arouse the anger of the statue-bashers – perhaps because of being a Cheviot sheep, the original wooly jumper, raised here to celebrate the town's (now defunct) woollen mills.

Repenting at this point of its valley flatness, the Annandale Way now climbs on a grand bit of old coaching road towards the river's source, at the rim of the Devil's Beeftub. This steep-sided hollow, sculpted by the Ice Age and the streams of today, was a handy place for hiding stolen cows in. And a great place to be even if you happen not to be a murderous bandit of the 16th century.

The Annandale Way and California's John Muir Trail are rather different walks. But they do have one thing in common. On each of them, the finish isn't at the end. Only slightly less inconvenient than the summit of Mount Whitney is Annandale Head, the source of the river at 450m on the Beeftub's rim. Failing a helicopter, you trickle down the Annan Water back to the handsome town of Moffat.

After all, everybody needs a second tasting of that triangular toffee.