After seeing the Malbork Castle, which usually takes a whole day, you can hop in a train and head back to Gdansk, or do what I did and spend a night in Hotel Zamkowy, which is located in the castle courtyard.
This just might have been the best hotel experience and value I have ever had in my life. For starters, this is a hotel with history... 500 year history! During the medieval times, it was used by the Knights of the Teutonic Order occupying the Malbork Castle as an infirmery. Not to worry though... you won't see any sick knights wandering the halls anymore. Rooms are small, but perfect. Dark wood walls, marble bathroom and a gothic pillar in the middle of the room give you an impression you're a guest of the Grand Master Ulrich von Jungingen. If you ask for a room overlooking the Nogat river, you'll have a spectacular view of some defense walls and pastures.
I booked the hotel through an online site:
Hotels Poland and paid $51 for it. The room prices vary by season, but you'll usually pay about $40-60 for a single, and $50-80 for a double. It's absolutely WORTH EVERY PENNY! Not only you get a premier location (Castle is eh... 10 yards to the left), you get to stay in a room with a history, and get a breakfast fit for a king. In fact, I have to mention the breakfast in its own paragraph.
Breakfast is served in the hotel restaurant, with huge wooden tables, you'd have difficulty touching hands with the person across from you. You get a breakfast set selection, and a large choice of breakfast pastries, beverages, and other goodies. It's also an awesome place for a drink after sightseeing in the castle on the previous night.
If you'd like to learn some more history of Teutonic Knights you can start at this
site. It depicts the greatest battle that ended their reign in Eastern Europe.
And by all means... Book a night in the hotel. You won't regret it, I promise.