I'm an American living in Germany and go to Kings as frequently as my wife allows.
Most have gave great advice taking a train into Weiden. But if you would like a bit more freedom, I would recommend renting a car from the airport and driving in. If you bust from a tournament, there isn't much else to do in the immediate surrounding area. There is a market (get cheap knock off goods), some restaurants, brothels, and a cpl of gas stations.
The town of Pilsen is about 45min away and a fun destination. A bit more metro than the countryside of Rozvadov, and it's where Pils beer originated from.
If you bring your GF/wife or for yourself, there is a popular spa town not too far away as well (Karlovary).
There is hiking and fishing for outdoors people.
Here are somethings that haven't yet been posted but are key...
1) If you are staying at one of the detached hotels (500m+) away from casino, do NOT walk to your room at 2am wearing dark clothes. It is very hard for motorists to see you. I almost wiped out a group of 3 (presume drunk) players as they were partially in my lane of travel... and NO street lights. I didn't see them until I was right there.
2) The free buffet is a great deal! Food is above average, but it isn't 5-star. It is definitely great value for the players that want a snack on a break or have a full blown meal. I have played some pretty large field tournaments at Kings and the buffet will get crowded during dinner break... #PROTIP: eat a little something before tournament, eat a little something on normal breaks, and AVOID it during dinner breaks (you're welcome).
3) Online poker is illegal in Czech (as I know it). So if you were hoping to grind online while away from the King's tables, you may want to consider staying just across the boarder in Germany (not necessarily illegal, more of a gray area and definitely within TOS).
4) If you don't like cigarette smoke... well... sorry. Although there is no smoking at the tournament tables, there is at the cash games. There is also smoking in the casino that you have to pass through to get to the poker area... and also people huddle around the main entrance to smoke and tell their badbeat stories in 35 different languages.
5) 420... I don't have alot of info here other than I've seen people passing around bananas in the park area in front of the hotel. I would keep it on the DL as I think it's still highly illegal in those parts and that would be a terrible badbeat story.
Hope that helps some when you travel to Kings. GL at the tables!