Day trip from Warnemunde
 

My parents and I will be on a cruise in July of 2014 and on our port of calls in Warnemunde. it looks really boring and I saw that Lubeck and Wismar are close and both look gorgeous. I also like the castles in Schwerin and Gustrow. Which ones can we see in 13 1/2 hours? What would you recommend? Thanks!!

Are you sure that you've properly investigated Waarnemunde-Rostock?

Their city site looks intriguing!
http://www.rostock.de/en/sightseeing/

Although, its true that Wismar also looks enticing.....

https://www.study-in.de/en/life/culture-travel--18200/

What form of transportation would you use to get around?
If by train, check www.bahn.de (check on english option) for travel schedule/times after entering 'to' and 'from' destinations.

For ex: time Warnemunde to Wismar is 1h43 min, changing in Rostock. Warn --> Schwerin is 1hr33 min, changing (again) in Rostock. Time to Rostock only is 20 minutes (bathing beaches).
Hope this helps, until you hear from someone local....

All in all Rostock offers far more than Wismar. It's not as picturesque, but more interesting IMO. Do give Warnemünde's old port/town area a try, too. It's lovely. Besides, closer than Wismar or Schwerin is Bad Doberan with a famous minster church.

Of course, nothing wrong with either Schwerin or Wismar ...