Both are quite often used, but if I were to say something about where I just went I'd would be 'I went somewhere beautiful' feels like you made a personal memory about that place while 'I went to a beautiful place' feels more like you went to some cool place.

I agree with Jaenri. The phrase "somewhere beautiful" sounds a little poetic or subjective. "A beautiful place" means that others would also probably find that place beautiful.

I think that we have to put the " Adjective " before the " Noun " . You said " I went to beautiful place " and I think that you should say the same " I think went to beautiful somewhere "