Picture from MaxiTurkey
Mausoleum of Halicarnassus also known as the Mausoleum of Maussollos
The tomb was built between 353 and 350BC in Halicarnassus (present Bodrum, Turkey) for Mausolus who was a satrap in the Persian Empire and Artemisia II of Caria, his wife and sister! What makes the structure extremely special is that it was not dedicated to the Greek Gods which is the case for many of the Ancient Wonders of the World (Wikipedia ).
How big was it? What did it look like? Research and find out!