Valka is a small Latvian town with a peculiar distinction: it shares a border — and a history — with the Estonian town of Valga, which sits immediately alongside it. The two towns were once a single settlement that was split when Latvia and Estonia established their border in 1920. After both countries joined the Schengen Area, the border became invisible again, and you can walk between Valka and Valga without noticing you've crossed from one country to another.
The Latvian side is the smaller of the two, with a handful of historic buildings along Rīgas Street and the Pēdele river running through the centre. The town's history as a teacher's seminary town gives it a slightly more civic character than its size might suggest, and a 19th-century viewing tower on Rīgas Street offers a panorama over both towns. St. Catherine's Lutheran Church, also visible from the main street, is worth a look.
Valka serves primarily as a transit town for travellers moving between Latvia and Estonia, and as a local service centre for the surrounding rural district. It is quiet rather than scenic, but the twin-city curiosity makes it interesting for an hour or two.