[2][3] Spruga is the last village on the sole road through the Onsernone Valley as well as the nearest settlement to the old thermal baths at Bagni di Craveggia where a 6-story hotel, now in ruins but open to the public, was built in 1819.

In the 19th century, visitors to the baths had to take an 8-hour carriage ride from Locarno to Comologno and then walk the last three to four kilometers on a dirt trail through Spruga with their luggage on mules or carried by locals.

The large Post buses have become a key feature of the region and a tourist attraction in their own right, as they traverse up and down the valley's narrow, winding road, honking their vintage-sounding horn to warn cars and pedestrians of their approach, often passing through villages with only centimeters of clearance from buildings on either side.

During the Ancien Régime, Spruga belonged to the Squadra of Crana which, together with the other villages of the valley (with the exception of Auressio), formed the medieval municipality of Onsernone.

The former Comune di Onsernone was divided into five squadre (localities) and 20 terre (fractions) until its dissolution as a political unit at the beginning of the 19th century: With the establishment of the Canton of Ticino in 1803, Spruga became part of the independent municipality of Comologno.