This hotel is located right next to the main square in Rostock and it's a perfect stop for one or two nights.

My husband and I stayed one night at this hotel. We found the rooms to be clean and reasonably priced. The Steigenberger Hotel is on the edge of a pedestrian square and is within walking distance to lots of outdoor cafes and small shops. Hotel rooms are typical European – small rooms, no air conditioning. We were able to open the windows and kept cool until about 3 a.m. That’s when the partiers got really loud and we had to close the windows. The staff was nice but spoke very little English. It is not a fancy hotel but I do recommend it because of its location.

We spent only one night there but it was the right hotel to choose.
The hotel is located in the heart of Rostock near the town hall (a very interesting building in this hanseatic brick style) and some steps away from the pedestrian area. Within walking distance you'll find the Warnow river (where Steigenberger has a great restaurant just on top of one of the old silo buildings - don't miss this place, excellent view combined with excellent food).
The rooms were nice, spotless clean, we asked for a quite room as this hotel is facing to a street with lot of traffic ). Breakfast buffet was great (yes, it's a typical Steigenberger and they definitely know how to make the guests satisfied) with cooked food as well (and a wide range of healthy items as well, fresh fruits, juice, muesli...).
The staff was very friendly and helpful (I forgot my contact lenses at home and they knew where to go to buy some...).
One point I always appreciate in a hotel: if you don't take something from the mini bar in your room, they don't charge it. (of course: this is what you could expect, always) It happend many times in other German hotels that I always found something charged from the mini bar at the time of check-out without a reason so I always look carefully at the bill but no problems here.
Another plus: W-LAN was for free in our room rate and worked well.
We'll definitely come back to this hotel!

The Steigenberger Hotel Sonne in Rostock is one of the nicer hotel properties in Rostock. Located directly across the street from the city's famous marketplace, a tram station, and the mouth of the city's pedestrian zone, the hotel is well situated for both business and leisure travelers. Rooms are a bit on the small side, but have nice amenities and are furnished in a sleek yet homey modern style. Many rooms overlook one of two busy streets. Especially in summer, when you're likely to have your windows open, the noise from the street and the restaurants below can be disturbing; it may be worth asking for a room that is not on the main street side. The breakfast buffet is wonderful--typically German with more choices than you can shake a stick at--and the restaurant and adjacent wine bar are fun, lively, and serve pleasant, if not earth-shattering, cuisine. Staff can be a little wishy-washy; when I checked in with piles of luggage, no one offered me a hand at the door or up to the room, and when I asked for assistance, the staff at the front counter seemed put out. By German standards, however, service was fine. I certainly prefer this hotel to the Radisson SAS because it is smaller and more intimate and I think the location is more convenient and charming. Also worth investigating for the more budget oriented traveler is the Hotel Kleine Sonne across the street. I haven't stayed there, but have been inside, and this seems like a very friendly, reasonable place directly across the street from the Steigenberger Hotel Sonne.