Describing Karviná as a spa town is really a little misleading. although there is a spa in the nearby Darkov, Karviná looks very different from your typical image of a clean, tranquil spa town. In fact, it is one of the centres of the (now declining) coal mining industry. There is a pretty townsquare, a little chateau and an animal park you can visit. The rest is all communist-built shopping centres and not so attractive hypermarkets that have sprung up in the 90s.
Going by bus is cheapest way to travel around Karviná. One bus ticket is about CZK 10 (approx. 0.35 €)
You can as well go by taxi, about CZK 20 per km (aprox. 0.7 €)