"to ittara": speaking of, talking of
This is an expression that emphasizes a feeling of surprise, disappointment, moving etc..
息子の部屋の汚いことといったら、ひどいものです。
Talking about the mess of my son's room, it's terrible.
その景色の美しさといったら、口で言い表せないほどです。
Speaking of the beauty of the scenery, it's impossible to express by words.
The scenery is so beautiful that I can't express by words.