This is the 9091st most frequent Polish word.
stuttgarcie
"Stuttgarcie" is not a standard Polish word; it might be a misspelling or refer to "Stuttgart" in locative case ("w Stuttgarcie" meaning "in Stuttgart").
'Stuttgarcie' is the locative case of the noun 'Stuttgart', used here to indicate the location where the subject (I) was last summer.
Byłem w Stuttgarcie zeszłego lata.
I was in Stuttgart last summer.
Here, 'Stuttgarcie' again appears in the locative case to denote the city where the uncle resides.
Nasz wujek mieszka w Stuttgarcie.
Our uncle lives in Stuttgart.
In this question, 'Stuttgarcie' is in the locative case, describing the place where the event possibly took place, related to the action of attending.