Here's a few
Croatia...Plitvice waterfalls
Plitvička jezera najstariji su i najveći nacionalni park Republike Hrvatske. Svojom iznimnom prirodnom ljepotom ovo je područje oduvijek pr...
np-plitvicka-jezera.hr
Italy...
Pisa, a lovely peaceful lakeside campsite (with regular bus service to Pisa)
https://www.lagoletamerici.it/en
Rome
Il Camping Village Roma Capitol è situato ad Ostia Antica, in un’area limitrofa alla pineta di Castel Fusano. Campeggio ecosostenibile con piscine e ristoranti vicino a Roma, ideale per famiglie.
www.campingcapitol.com
A short walk to the tram station linking it to central Rome, a Roma 48 hours pass is great, available from the campsite reception.
Ljubljana, Zagreb, Bratislava and Budapest all have camp sites (city camp) nearby... Budapest and Ljubljana are fabulous.
Budapest...
hallercamping.hu
Poland
Krakow Salt mines
Masz ochotę na spacer wśród solnych dzieł sztuki? Wybierz Trasę Turystyczną!<br />Wolisz wędrówkę po zakamarkach podziemnego świata? Wyrusz na Trasę Górniczą!
www.kopalnia.pl
and
Bialowieza (North east) Poland.
The Białowieża Forest World Heritage site, on the border between Poland and Belarus, is an immense range of primary forest including both conifers and broadleaved trees covering a total area of 141,885 hectares. ...
whc.unesco.org
Most places in Germany are well worth visiting.
I could suggest hundreds of other places, but the fun is finding stuff along the way .
Good luck