" We stopped at an ice cream shop on the way back from the beach."
Ice cream shop and beach are both common nouns because they don't name a specific ice cream shop or beach. Mmm, Bi-Rite.
Note: technically, ice cream in this example functions as an adjective that modifies shop—what kind of shop is it? An ice cream shop. But for all intents and purposes, we'll say ice cream shop is a noun phrase.
" The controversial rapper's tour stopped in fifty-five cities across the country."
Since rapper doesn't name a specific MC, it's a common noun. Ditto for tour, cities and country: they all name general things or places.