National parks are key for conserving nature. But they are also important to people, who receive physical and psychological benefits from interacting with nature during recreational activities. Nevertheless, national parks are under pressure from human needs for land and development and this is challenging their existence. Understanding people’s feelings about, and preferences for, parks is key for promoting socio-political support and help foster conservation actions that support nature. Social media platforms have become popular means for sharing experiences about nature when visiting national parks. Compared to other methods, such as traditional surveys, social media data provide rapid and cost-effective opportunities to understand how visitors perceive national parks and what experiences they consider worth sharing. In this study, we investigated what visitors posted about on Instagram in four national parks in South Africa and what was the sentiment attached to these posts. We found that visitors tend to share positive experiences, mostly related to emotions such as joy, anticipation, trust and surprise, when posting in the parks. Appreciation of nature and a diverse set of aspects related to it (e.g. animals, beach, ocean, activities to enjoy nature, geographical landmarks and iconic places) were popular on social media posts. In addition, the aspects featured on social media were park-specific and visitors posted either about wildlife watching or scenery experiences according to the national park visited and its characteristics. Findings highlight the societal role of national parks in providing visitors with opportunities to develop positive connections with nature through recreation. Social media data may be used to assess how visitors perceive parks and what features they share as symbols of a satisfactory experience. In addition, social media can help understand how the profile and image of national parks is constructed in the virtual social environment, which is increasingly playing a significant role in shaping public reputations of places, travellers’ behaviour, choices and expectations.