La Sagrada Familia, Barcelona. This place is on my bucket list to visit. My girlfriend is a big fan of his architecture and I'm sure we would both be stunned with silence when we do see it.
The Versailles gardens took 40 years to complete; Louis XIV valued them as much as the palace.
Day (1) Ancient Rome - Colosseum. For great views head into Parco del Colle Oppio and up Colle Oppio Hill right above the metro station, or into Parc del Colio up Colle Celio Hill opposite the Palatino and Collosseum exit.