You'll probably see Holy Trinity Cathedral across town before you actually find this incredible place of worship. Peek inside if it's open or just admire the facade from outside.
You'll have no end of sightseeing choices when in Arada. Holy Trinity Cathedral is a great place to begin here, but there are numerous other interesting sights to check out. African Union Headquarters, Edna Mall, and Addis Ababa Stadium are near the principal church and will fill in your day nicely.