Catherinethal ("Catherine's valley") is a Petrine Baroque palace of Catherine I of Russia in Tallinn. It was built after the Great Northern War to Nicola Michetti's designs by Gaetano Chiaveri and Mikhail Zemtsov. In the 20th century the Estonian version of the name, Kadriorg, gained currency and came to be applied to the surrounding district.
After the successful siege of Reval in 1710 Peter the Great of Russia bought a Dutch-style manor house at Lasnamäe for his wife Catherine. The house today is the result of a drastic renovation ordered by Nicholas I of Russia in 1827.
The new palace was started on 25 July 1718. Peter and Catherine visited the unfinished residence on several occasions, but after the emperor's death in 1725 Catherine showed no interest in the seaside property. The great hall with Catherine's initials and profuse stucco decor (attributed to Heinrich von Bergen) survives, but many other interiors have been altered. The gardener Ilya Surmin was responsible for the flower garden with two fountains and the so-called mirage garden on several levels. The layout of the park shares similarities with that of Strelna.
The palace currently houses an art gallery. The KUMU Museum is sited in the park.
First record of Kastelholma (or Kastelholm) castle is from the year 1388 in the contract of Queen Margaret I of Denmark, where a large portion of the inheritance of Bo Jonsson Grip was given to the queen. The heyday of the castle was in the 15th and 16th centuries when it was administrated by Danish and Swedish kings and stewards of the realms. Kastelhoma was expanded and enhanced several times.
In the end of 16th century castle was owned by the previous queen Catherine Jagellon (Stenbock), an enemy of the King of Sweden Eric XIV. King Eric conquered Kastelholma in 1599 and all defending officers were taken to Turku and executed. The castle was damaged under the siege and it took 30 years to renovate it.
In 1634 Åland was joined with the County of Åbo and Björneborg and Kastelholma lost its administrative status.