Day 3 on italki!

Today I'm in Terni for work. Terni is a city situated about 100 km from Rome. (Terni) It is famous for its waterfalls ("Cascate delle Marmore"), for its steel plant and because it's the city of St. Valentine.

Terni is a very particular city and its citizens are very friendly, it's a pity that I must work and I can't visit this beautiful city.

Ciao!
Cris

I put a period instead of the comma, because you are repeating the city's name right away.  It sounds heavy to repeat the name twice in the same sentence, so if you want to join the two sentences into one you could say, for example:  "Today I am in Terni, a city situated about 100 km from Rome, for work."

Excellent work!

Day 3 on italki!

today I'm in Terni for work. Terni is a city situated about 100 km from Rome. Terni is famous for its waterfalls ("Cascate delle Marmore"), for its steel plant and because it's the city of St. Valentine.

Terni is a very particoular city and its citizens are very friendly, it's a pity that I must work and I can't visit this beautiful city.

Ciao!
Cris

Good job! This article is 99.9% correct.