"is" powinno byc na koncu
If you WANT to know how exciting A place to live in the city
called “Polish Venice" IS - come to Wrocław straight away!
Poza tym zdanie jest niezgrabne bo ma dwa slowa, ktore znacza to samo: "place" i "city".
Moja propozycja:
If you want to know how exciting to live in the city called “Polish Venice" is - come to Wrocław straight away!
Lub:
If you want to know how exciting the city called "Polish Venice" is to live in - come to Wroclaw straight away.