Can I say to a doctor:
Always nice when I visit your clinic!
Is it correct to say 'Visiting your clinic is always nice!'?
It's grammatically correct.
Which one is grammatically correct?
Both yours and Matthew's are correct.
You must be the only person on the planet who has ever wanted to express such an opinion about a visit to the doctor!
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.