Dear Priscilla,
If you have only one day available for a day tour from Addis Ababa, following are few interesting places to visit: -
1. Visit the unique still operational church of Adadi Mariam which is carved out of a single piece of rock in the 13th Century AD, and steles of Tiya (14th Century AD and UNESCO World Heritage Site). To visit these places you will drive 190 km in total and you drive southwest of Addis Ababa via the town of Alem Gena. If you are doing this tour on Thursday or Sunday, check out the interesting cultural weekly held market of the Oromo people at the town of Adadi. Along the way, you can also stop to visit the archaeological site of Melka Kunture.
2. Drive 100 km north to visit the biggest monastery in Ethiopia - Debre Libanos Monastery (13th Century AD), enjoy the great view of the Jemma Valley, see one of the endemic mammals of Ethiopia - the Gelada Baboons, and visit the Portuguese BRIDGE (16th Century AD).
3. Drive 50 km east of Addis Ababa on the Express Way to visit the five crator lakes, bird life, water sports, etc
Regarding local food, taste the varieties of Ethiopian deliciously hot meals served in one plate. The vegetarian one is known as "Yestom Beyaynet", and the non-vegetarian dish is called "Yefisik Beyaynet"
Enjoy your tour!