There is plenty of beautiful views of Prague from Letná all along the ridge. You can come here any time, day and night. It is usually pretty crowded area here, however it is spatious, so everyone can find a place. Weather as a part of a walking tour or to grab something and sit down for some time to enjoy the views.
How to find Letná views:
You can come here via stairs ´to Stalin´ from the Old Town or from the Letná field from the opposite direction.
GPS coordinates of Letná views: 50.093550, 14.412703 Take me there!