Re: Madrid para una noche
If I only had one day in Madrid and wanted to be outdoors I'd just chill in Retiro (always so much going on there) then make my way up to Sol, Plaza de Isabel II, then onto the Palace (it's all within walking distance). Also the Temple of Debod is pretty cool and is in a park with stunning views of the Palace and Casa de Campo.
As far as going to eat you can find so many nice little places in La Latina or on the streets just off Sol. Plaza Mayor too.
El Tigre is a pretty cool bar/restaurant (the tapas is that huge that it counts as a meal), just off Gran Via (it's well known so it's easy to ask people for directions). It gets absolutely packed which makes for a great atmosphere and very easy to just start chatting with just anyone.
If you like Opera the Teatro Real are doing 90% discounts on various days.