We will be visiting Beijing for 4D5N. Is it worth taking a day trip to Tianjin?

Hello,
For 3 days , we will see Beijing. We have one day available when we could either go aroung Beijing or take the bullet train to see Tianjin. Is it totally worth it? Is there somethings unique to see?
If so, what are the top 3 things? How to go about in Tianjin ? Is it exoensive?
Please advise
Samy