<Tr> <Td> Knowth </Td> <Td> </Td> <Td> Ireland </Td> <Td> Europe </Td> <Td> Between 2500 - 2000 BC </Td> <Td> Passage grave </Td> <Td> </Td> </Tr> <Tr> <Td> Pyramid of Khafre </Td> <Td> </Td> <Td> Egypt </Td> <Td> Africa </Td> <Td> c. 2500 BC </Td> <Td> Tomb </Td> <Td> One of the Pyramids of Giza . </Td> </Tr> <Tr> <Td> Pyramid of Menkaure </Td> <Td> </Td> <Td> Egypt </Td> <Td> Africa </Td> <Td> c. 2500 BC </Td> <Td> Tomb </Td> <Td> Menkaure was probably Khafre's successor . </Td> </Tr> <Tr> <Td> Dowth </Td> <Td> </Td> <Td> Ireland </Td> <Td> Europe </Td> <Td> 2500 BC </Td> <Td> Tomb </Td> <Td> The cairn is about 85 metres (280 ft) in diameter and 15 metres (50 ft) high . </Td> </Tr>

How old is the oldest man made structure