Can I make a day trip from Xi'an to Shaolin temple and Longmen Grottoes in a day?

Hey, one day is enough to cover both of them, but it can be tight to get back to XA. It will be cold and dry during the Christmas. You should wear down jacket, thermal long john and boots.

What bus shall I take from Luoyang longmen station to Shaolin Temple and onwards to Longmen Grottoes? What will it cost and how long is the journey?

Well, you are suggested to Longmen Grottoes first. Take Bus 910 from Luoyang Longmen Station to Longmen Beiqiao Dong, and then walk southwest for 10 minutes to the grottoes. It takes about 30 minutes and CNY2.

Then, I was told there are regular buses from the parking lot of the grottoes to Shaolin Temple, which takes about 70 minutes and CNY110 (including the ticket fare).