Another option to get to Decin - but also to explore the regions upstream and downstream the Elbe/Labe river - is by boat. They run downstream between Decin and Hrensko, a few even to Bad Schandau (Germany). Other boats go up the river to Usti n. L. and beyond to Melnik e.g.
Be forewarned that service is infrequent and most boats only run in summer. The focus is really on enjoying the boat ride, spending time gazing at the beautiful scenery, and not on getting as fast as possible to your destination.
Prices are very reasonable. The ticket Decin - Bad Schandau and back is e.g. CZK 280 (about 12 Euro).
In spring 2011 I planned on visiting Decin and thought "Why not cycling?" It is just 21 km from Bad Schandau to Decin, a well maintained, flat cycling trail along the river. And the scenery is gorgeous! This trail is a section of the very popular "Elbe cycling trail" which leads from the Krkonose mountains along the river to Hamburg.
Trains also run along the river so you can take a (regional) train to the station where you want to start and hop on another train in case you're exhausted. Very convenient!
Expect a lot of traffic on this trail. Beside the cyclers you will also see walkers, skaters, rollerbladers. No cars, of course.
There are benches and picnic places every couple of kilometers. More frequent on the German side, less so on the Czech side.
Decin has a pretty good bus network. Unfortunately the website is only in Czech - but the other link below takes you to the section of the website where you find maps and timetables. "Jízdní řády" means timetables, "Plán linek" means maps. "MAD" refers to the buses in the city, "doprava" is for the surrounding region.
In 2011 a single trip (city) for adults was CZK 20 (about 0.80 Euro). A day ticket (city) was CZK 50 (about 2 Euro). Buy the tickets from the driver.
The main bus station is a bit south of the main train station but most buses stop also at the train station (hlavni nadrazi).
As the most attractions are not *that* far from the train station you might consider walking to them, but maybe better take the bus back.
Decin has good train connections in all directions. Every two hours an international train between Prague and Dresden (-Berlin) stops in Decin. These trains run along the Elbe/Labe river valley - a very scenic ride.
There are also trains to Prague that start in Decin and run via Usti n. L. Regional trains run from Decin to Teplice v Cechach (the spa town, see my page) and via Benesov and Ceska Lipa to Liberec (see my page on this town also). Every two hours there are regional trains across the border to Bad Schandau in Germany. From the stops along the way you have easy access to the National Park.
The building of the main train station in Decin (hlavni nadrazi) is nicely restored. The ladies at the ticket counters speak Czech, a bit English and a bit German.
The best way to get to decin is to travel by car from dresden (45 km) or from Prague (120 km). Rods are in good condition and very picturesque. The exact directions and also train time table you may find at www.pbrana.cz