Fortunately, this city is often overseenlooked by international tourists, which makes it much less crowded than Florence or Rome. Fortunately, this city is often overlooked by international tourists, which makes it much less crowded than Florence or Rome.

Overseen = they supervised or managed it Overlooked = they failed to notice or think about it

Fortunately, this city is often overseenlooked by international tourists, which makes it much less crowded than Florence or Rome. Fortunately, this city is often overlooked by international tourists, which makes it much less crowded than Florence or Rome.

To overlook means to ignore or not see, oversee means to manage or monitor.

Its university is {the city's | its} hallmark, accommodating almost 100.,000 students and being the oldest university in continuous operation in the world by, having functioninged for over 900 years. Its university is {the city's | its} hallmark, accommodating almost 100,000 students and being the oldest university in continuous operation in the world, having functioned for over 900 years.

Its university is the city's hallmark, accommodating almost 100.,000 students and being the oldest university in continuous operation in the world by, functioning for over 900 years. Its university is the city's hallmark, accommodating almost 100,000 students and being the oldest university in continuous operation in the world, functioning for over 900 years.

In English, the '.' is to separate the decimal. It's called 'the decimal point'. eg pi ~= 3.1415. To make large numbers easier to read, we use the ','. This sentence is a little too long for English standards. I would probably write the end as "...in the world. It has been functioning for over 900 years."

All together, they cover almost 40 kilometers only in centro storico (in the city center?), serving as effective protection from both rain and sun. All together, they cover almost 40 kilometers only in centro storico (in the city center?), serving as effective protection from both rain and sun.

What is “centro storico”? If it’s the city center, then id suggest using this English term, as it will be understood by more readers. “they cover almost 40 kilometers only in centro storico” - this means that porticos don’t exist outside centro storico. Do you mean that “they cover almost 40 kilometers in centro storico alone” (only counting the porticos in centro storico, not any that might exist outside that area)?

All together, they cover almost 40 kilometers only in cCentro sStorico alone, serving as effective protection from both rain and sun. All together, they cover almost 40 kilometers in Centro Storico alone, serving as effective protection from both rain and sun.

In English, we usually capitalize 'proper nouns', so any location name should be capitalized. I usually don't bother when texting with friends, but for formal written English, it is required.