Liechtenstein
A 135-metre timber tunnel over the Rhine; somewhere inside it, you change countries.
The Alte Rheinbrücke is a covered timber tunnel running 135 metres from Vaduz to the Swiss village of Sevelen, the last wooden bridge left standing over the Rhine. There is no checkpoint, only plank echo and river noise, and somewhere over the grey water you pass from Liechtenstein into Switzerland.
A ferry served this crossing until the first wooden bridge went up in 1871; today's Howe-truss span was finished in 1901 by the bridge-builders of Azmoos on its predecessor's reinforced piers. The river kept pressing against the corrected channel: the first bridge had to be raised twice, and after the Schaan dam burst of 1927 the present one was lifted again to clear the water. Motor traffic left long ago for the concrete bridge upstream; since 1973 the timber tunnel has belonged to walkers and cyclists, Liechtenstein protected it as a monument in 1981, and a full renovation followed in 2009-10. Sevelen's municipality calls it the last witness of wooden bridge romanticism on the Rhine, and the Vaduz circular trail threads it into the capital's sights, so an international river crossing on foot fits inside an ordinary morning.
Solo
Crossing a border alone on foot, inside a wooden tube that hums with the river underneath, is a small thrill that no busy attraction can copy.
Couple
Walk the span at dusk when the timber holds the day's warmth, stand over the Rhine with a country on either side, and wander back into Vaduz for dinner.
Family
Children can stand with a foot in two countries halfway along a bridge that has carried this crossing for well over a century; the deck is closed to cars entirely.
Friends
The two-country picnic writes its own script: provisions from Vaduz, 135 covered metres of timber, plus an argument over which bank of the Rhine has the better view.
After the crossing, climb to Restaurant Torkel on the Vaduz slope, where the estate wine on the list grows on the hillside above the dining room.
Or stage the two-country lunch yourself: provisions from Vaduz, 135 covered metres of timber, and a riverside picnic on whichever bank you prefer.

Schellenberg
Liechtenstein
Schellenberg keeps two ruined castles on one ridge; the bigger one lets you barbecue inside.

Liechtenstein Trail
Liechtenstein
Walk an entire country in five days, 75 kilometres from Balzers to Schaanwald.

Vaduz
Liechtenstein
A capital small enough to cross on foot, its reigning prince asleep in the castle overhead.

Triesenberg
Liechtenstein
Seven centuries on, this mountainside still speaks the Walser German its settlers carried from Valais.