Ex.1
Dear Elena,
How are you? Now I'll describe my favourite city, London. London is the capital and largest city in the UK; it is situated in the southern part of Britain. About 8 million people live in London. There is a mild climate: winter can be very wet and cold, in summer there are hot days with high humidity. 
There are lots of beautiful and interesting places.
The Tower of London is a complex built in the Medioevo and it is mixture by different buildings strengthened. The tower is protected from the beefeaterses. The most ancient visible structure is 'White Tower'. The tower was a palace and a prison. Now it is a museum. Near the Tower of London you can admire the Tower Bridge; it looks old but it's one of London's newest bridges. It has two levels, one for people and one for traffic. Another important bridge is the Millenium Bridge, which is London's newest bridge. It is only for people. Along the River Thames ( it runs through the city ) you can see the Houses of Parliament; there is also the Big Ben, which isn't the name of the famous clock but the bell inside the tower. You can admire London Eye, too. It's 135 metres high and the viewes from the top are fantastic. 
In my opinion London is fabulous, also because there is the residence of the Queen, Buckingham Palace. Every morning a crowd of tourists stand outside the palace for hours tp see the Changing of the guard.
There are lots of museum, like the British Museum, Madame Tussaud's and lots of cathedrals, for exemple Westminster Abbey, which is the traditional place of incoronation and burial site for english monarchs. There are some famous streets and squares in London. Oxford, Regent and Bond street are important streets, with their famous department stores. Trafalgar Square is a large square that commemorates the Battle of Trafalgar. On the northside of Trafalgar Square there is the National Gallery. Picadilly Circus is a place for entertainment and shopping. 
There are some beautiful parks, too, like Hyde Park and Green Park.
In order at Greenwich there is a line on the ground which marks 0 longitude. The you can stand with one foot in the estern hemisphere and the other in the western hemisphere. 
So, London is a wendorful city and I can't wait for return there. Write me back soon, bye.

Ex.2
T: Guys, we have to organize a school trip!
G: Sure. But where are we going?
T: We have to organize a trip that is in connection with the topics that we are dealing. Have you got any ideas?
G: Why don't we go to London? It is a beautiful city. We can admire the Tower of London for exemple. We studied that the tower was a palace and a prison. That trip will be useful to better understand England's history.
T: Good idea! The trip could take us two days, which are parfect to visit the most important London's places. 
G: Let's go to London!
T: Be quiet guys... It's only an idea!