In Xcode 6.3 and later (including Xcode 7 and 8), console output appears in the Debug area at the bottom of the playground window (similar to where it appears in a project). To show it:

  • Menu: View > Debug Area > Show Debug Area (⌘⇧Y)

  • Click the middle button of the workspace-layout widget in the toolbar

workspace layout widget

  • Click the triangle next to the timeline at the bottom of the window

triangle for console

Anything that writes to the console, including Swift's print statement (renamed from println in Swift 2 beta) shows up there.

In earlier Xcode 6 versions (which by now you probably should be upgrading from anyway), show the Assistant editor (e.g. by clicking the little circle next to a bit in the output area). Console output appears there.