Kazimierz Dolny is beautiful with a ton of history. It's definitely worth the trip. Also, ruins of the Janowiec castle are just across the river and open to tourists, and Naleczow, a very pretty and historic resort town, is nearby. Naleczow may actually be a bit closer to Warsaw than KD is.
However, note that it takes 2 hours by train from Warsaw to Pulawy, and then 45 min-hour or so by city bus from Pulawy to KD, as there isn't a train station in KD.
HOWEVER, if you take travel a bus (halobus, etc there are tons of different companies), you can go straight from Warsaw to to KD, and the whole trip should take about 2.5 hours. It's more convenient then dealing with the trains and then the city bus, and it's probably cheaper too.
I hope to go to a place where it is just max 2 hours from warsaw so that travel time is shorter and visit time is longer. If 3 hours, I heard Torun is a nicer town to go to. So maybe I need to reconsider about going there.
I try to google again and find that there are few National Park not far from Warsaw. Maybe going out into nature is worth it?
Białowieża National Park. It will take three hours to get there (unless you take a helicopter trip), but it's worth it. The park is great at any time of the year, except high summer, when the mosquitoes rule. You have to pay to have a guided tour of the 'Strict reserve', which is the last untouched fragment of primeval European lowland forest. There are also excellent restaurants, e.g. Carska.
Toruń is definitely do-able as a day-trip from Warsaw, but it would a long day. It is not far if you look at its location on the map, but the connections to get there are the main issue. I went there by bus when I spent a week in Warsaw. The trip there took some 3-4 hrs one way (I could be off; I vaguely remember how long exactly) and included a stop where I had to transfer buses, but that was almost 10 years ago so maybe the connections improved since that time (I would definitely do some research/planning to avoid potential frustration). I have no idea if there are any tour companies in Warsaw that organize tours to Toruń. Toruń is mostly famous for Copernicus (there is a statue of him and a museum in the town). I think the old town is also a UNESCO heritage site. You can easily find information online about the attractions there.
