Dear Mike, (wystarczy przecinek)
Greetings from Madrid! (nie daje sie kropki, jezeli juz uzyles wykrzyknika, czy innego znaku interpunkcyjnego) The weather is very hot here. I'm having a wonderful time. I'm staying with my friend Carlo.
I've been here since last Monday and I've already done {a} few things. I've already visited the Prado Museum. I visited it last Tuesday. It's {a} fantastic place! I saw some beautiful paintings there. I've also seen the Palacio Real. I visited it yesterday. The state??? rooms were magnificent. I like Spanish {cuisine}. I went to "Lhardy" restaurant last night with some friends. The food was just delicious. You should try paella.
There are a lot of things I haven't done yet. I haven't been shopping but I want to go to {} Rastro flea market to buy some souvenirs. I haven't {} been to the opera {either}, so I'm going to go there tomorrow to see "Carmen".
Madrid is a marvellous city - you must visit it one day. I'm returning to Poland on Saturday this week, so I'll call you then.
Best wishes,
Zdzichu