I want to visit Forbidden City in Beijing from Tianjin. Can I have a round trip in one day if I travel by train?

Yes, you can have a round trip within one day. The intercity bullet trains between the two cities are very frequent and convenient.

The train departing from TJ will take you to Beijing within around half an hour. You will arrive at the local South Railway Station, where you can take subway line 4 to Xidan Station and then transfer to line 1 to Tiananmen East. Get out from Exit A, you can walk to the Forbidden City. For the back journey, you can use the same way.

Dear Peter
Thanks a lot for so comprehensive information.