From the Wikipedia page 
Valka (About this sound pronunciation (help·info); German: Walk) is a city and municipality in northern Latvia, on the border with Estonia along both banks of the river Pedele.
Valka and the Estonian town Valga are twins, separated by the Estonian/Latvian border but using the slogan "One Town, Two Countries". The border dividing the Livonian town of Walk was marked out in 1920 by an international jury headed by British Colonel Stephen George Tallents. With the expansion of the Schengen Agreement and abolition of the Estonian/Latvian border in 2007, it was announced that common public bus transport would be established between Valka and Valga. Also, all border crossing-points were removed and roads and fences opened. In 2016 it was announced that due to better welfare and higher salaries in Estonia, many Valka inhabitants have registered themselves as inhabitants of Valga.