A great park, a couple of blocks down from the Plaza de España... the view of southern (?) Madrid is lovely. Wonderful place to hang out when the weather's right.
Be there at sunset any time in May if you want to see couples getting their wedding photos taken. Watch the photographers struggle to keep the other wedding parties out of their frame... well, I find it amusing. :-)
The temple that the park is named for was donated by the Egyptian government, it's pretty unique. Read about it here: en.wikipedia.org/wiki/Templo_de_Debod