a Kingsized bed.. a room lit with candles... a classical song.. playing to smoothen the romantic ness... and have candy... on the bedside table.. to feed your fiancee xD
Take your partner to a nice hotel, arrange rose petals to be sprinkled over the bed and get champagne delivered, it can be pricey but it will be worth it.
x
That would be roof top right underneath the stars, make it comfy though, nothings as boring as a romantic but uncomfortable romantic encounter. find out what her idea of romatic, people differ you know.