Simplify the following text for a Grade 13 native English-speaking person.
Original: Tongariro National Park , in particular , is one of 27 World Heritage Sites that is of both cultural and natural significance , while four of the South Island national parks form Te Wahipounamu , another World Heritage Site .
Simplified: Tongariro National Park is one of 27 World Heritage Sites that is of both cultural and natural significance , and four of the South Island national parks form Te Wahipounamu , another World Heritage Site .