Chehelsotoon Museum - as spelt at the main entrance where you need to get the ticket from - can be spelt in more ways than one. Some refer to it as Chehel Sotoon, others as Chehel Sotoun, and may be as Chihil Sutun as well. This is always the case when one translates the name and spelling of the places from one language into another, and especially more so in this case as it involves a language that uses a different set of characters altogether. In Persian, it is spelt as "چهل ستون".
Why forty columns?
Because Chehelsotoon, which is a pavillion, has many columns; and in Persian, forty is defined as many. Incidentally though, the pavillion has 20 columns and when seen from the front across the pond, these columns are reflected in the pond, giving the impression of 40 columns in total.
Like Hasht Behesht, Chehelsotoon is surrounded by a garden, and the garden is listed as one of the "Persian Gardens" recognised by UNESCO as a World Heritage.
Chehelsotoon was built by Shah Abbas II in mid-17th century. It was used by the Shah to receive and entertain his guests either on the terrace which has a beautiful facade like shown above, or in one of the stately halls as shown below, where the walls and ceiling are highly ornate.
The inside of the dome
There's no doubt that the place was built to impress, right? :-)