Romantic & Passionate:
* Rendezvous
* Tryst
* Encounters
* Assignation
* Amorous meeting
* Secret meeting
* Stolen moment
General & Neutral:
* Meeting
* Gathering
* Date
* Appointment
* Get-together
More Specific & Descriptive:
* Candlelit dinner
* Moonlight stroll
* Park picnic
* Dancing night
Informal:
* Hangout
* Hook up (can be considered slang)
The best word will depend on the specific situation you're describing.