Take the train from Dresden, upstream along the bank of the Elbe. This service operates half-hourly, servicing, eg., Pirna, Bad Schandau; from Pirna, the line runs next to the river, very scenic. The trains terminate alternately at Bad Schandau, or (a few minutes further on) Schöna. If you continue to Schöna, the station nestles on the bank of the river, but without Schöna itself being evident. However, down steps directly from the station is a ferry jetty, the ferry for which will take you across the river to Hrensko - welcome to Czechoslovakia!
Hrensko is a small village, running along the road following a stream which flows into the Elbe - you will hence be walking directly away from the Elbe. The first sight is of a canyon of stalls, end-on-end, selling all manner of goods, principally clothing (it seemed); where they get sufficient custom for all this stuff, goodness' knows. Keep walking, and after a while the stalls thin out and you get to a normal townscape which includes many restaurants, most with terraces, many overlooking the stream referred above. It is very pleasant (once you keave the stalls behind).
We had lunch in the Hotel Praha, and very satisfactory it was, too; it was also extremely good value.
After lunch, you can walk back down to the ferry, cross to Schöna station and get the train back to Dresden - train leaves hourly, takes about one hour to get back to Dresden, half of which is along the river bank. Enjoy your visit to Czechoslovakia!