Alright, let's fill in the blanks using the present continuous tense, which is formed with 'am/is/are' + verb-ing. Here are the sentences:
Dear Sandy, Greetings from St Petersburg! We are here for the lovely Golden Autumn. Together with the residents, we 1) **are enjoying** the last days of sunshine. This is a quiet time of year, and so Betty and I 2) **are enjoying** our stay. Today we 3) **are not visiting** historical monuments. We 4) **are relaxing** in the gardens of Catherine’s Palace outside the city. It is Saturday, so many families 5) **are walking** in the woods and 6) **are having** picnics on the grass. Betty 7) **is resting**. She 8) **is drinking** a cool drink by one of the fountains. I 9) **am writing** a few postcards. When 10) **are you planning** to visit this wonderful city?
Here are the answers: 1. **are enjoying** 2. **are enjoying** 3. **are not visiting** 4. **are relaxing** 5. **are walking** 6. **are having** 7. **is resting** 8. **is drinking** 9. **am writing** 10. **are you planning**