Zegaani Monastery is located in Gurjaani district of Kakheti region. It includes 2 churches from 5th century and 6-7th centuries. The main church has frescoes from XVI-XVII centuries. The monastery has a beautiful garden which is especially beautiful in the beginning of November (end of October) during autumn season.
You can visit Zegaani Monastery in any tour of Kakheti region, even if you visit it for 1 day, its always beautiful and tranquil. It can easily fit if you go to Sighnaghi but first visiting Numisi winery Zegaani is very near from central road and you can easily find peace of your soul. But my suggestion is the following if you have more time to explore unknown Kakheti.
Sights You should visit
Shios Marani in Ruispiri Telavi, Vazisubani Monastery (recently renovated and not sure about its current effect) and Vachnadziani Kovlatsminda (allmighty) if you have jeep and want views, Gurjaani Kovlatsminda (2 domed cathedral) if you have time.
Trekking Route of Cheremi
For Trekking I think the best is hike to Cheremi old city and Cheremi Lake. High above in the ridge, Cheremi has all what you may wish for: panoramas, forests, hidden churches in the forests and amazing old city ruins which are one of the best archeological monuments of Georgia from 5th century. Please contact me for more info if you happen to read the article before I have posted gps trial.
Please see the map here: