"World class" monuments to visit in April

I am trying to plan a month long backpacking trip in April, such that:

1. It has either rich cultural heritage or natural beauty. I am after "world class", breath-taking monuments (so for instance I wouldn't consider Armenia - ignoring the fact that its in Europe - even though it has a couple of really nice monasteries). I know its subjective criterion, but I don't really know how to phrase it any better.
2. April is a reasonable month to visit (I am thinking mainly about climate)
3. Is malaria-free
4. Is at altitude <3000m (I will be traveling with small children)
5. Is reasonably safe (e.g. I wouldn't consider Syria at the moment)
6. Is "exotic" for an European (so I rule out the whole of Europe, USA, Canada, Australia and New Zealand)

I would also like to exclude countries we have visited recently: Morocco, Tunisia, Turkey, Thailand, Malaysia.

I will be traveling from London. Budget is a secondary issue, but we probably can't afford super expensive countries, e.g. Japan.

Hopefully I gave enough criteria to make this question interesting.