On a map of Tallinn, this is the large green area to the east of the town. Kadriorg is Estonian for Catherine's Vale.
The park was created by Tsar Peter the Great soon after Russia had seized Estonia from Sweden in 1710. He named his Summer Palace after his wife Catherine, in Russian Yekaterina. 
She was not in fact a Russian. Originally named Martha Skavronska, she was the daughter of Latvian peasants.She worked her way up through several Russian noble families, as a mistress or servant or both, before being passed on to Tsar Peter by his best friend, Prince Menshikov.
Russian royalty soon lost interest in the park at Tallinn. Even in Peter's day it was used so little that it was generally open to the public. Partly as a result, the area became popular among wealthy local families and there are fine houses and villas in its leafy streets.
It also contains more museums than any normal person would want to visit in a month. However at least two of them - the National Art Museum in its new building and its foreign art collection in Kadriorg Palace - are well worth seeing.
The easiest way to get there is to take Tram number 1 from Fat Margaret's Tower. The destination will be marked Kadriorg but get off at the fourth stop and walk up L. Koidula street. 
Many of the houses on this street date from the 19th century. The villa at number 10 is a fine example of Art Nouveau.
Halfway up Koidula, where the park begins, is an area known as the Russian village, which contained small wooden houses where the servants of the palace lived. Unfortunately the houses that have survived are in pretty poor shape.
Nearby is the symmetrical swan pond, a favourite place among the people of Tallinn for summer outings. A promenade leads past it to Kadriorg Palace. The main hall of the Palace is a gem of Russian baroque architecture.
The dull rectangular building just beyond the palace is where Tsar Peter lived while his palace was being built. It doesn't look like much on the outside but inside are many original pieces of furniture used by the Tsar.
The massive modern green building against the cliff in this corner of the park is the new Kumu Art Museum of Estonia. Even if you've had your fill of museums by now, it's worth visiting for the nice cafeteria on its ground floor.
At the end of a long avenue leading from the palace to the sea, you may be able to make out a statue. This is Rusalka, which commemorates a Russian warship of that name that sank in 1893 en route to Helsinki.
The kitsch figure of an angel pointing at the waves is regarded by Estonians as a classic but is not worth crossing the park for, unless you are in desperate need of exercise.
