We enjoyed our stay at Carla's guest apartment. This is a surprisingly bright basement unit, and stayed comfortably cool during the hot temperatures while we were in Seattle. Check-in and access was painless with the keypad lock. We really appreciated being able to park in the driveway for loading/unloading all our infant gear since street parking in Ballard can often require walking a ways from car to house.
If you're not a heavy sleeper definitely bring good earplugs and/or a sound machine. Guests coming and going from the unit upstairs in the middle of the night/early morning can be noisy as this is an older house.