I can provide information on the attractions you mentioned in terms of natural beauty, cultural value, local people, various activities, accommodation and services, and cuisine.

1. Phong Nha-Ke Bang National Park: This park is known for its stunning natural beauty, including a vast network of caves and underground rivers. It is also home to many rare and endangered species of plants and animals. Visitors can explore the caves, go trekking, and enjoy other outdoor activities. The local people are friendly and welcoming, and there are many options for accommodation and dining.

2. Hue Imperial Citadel: This UNESCO World Heritage Site is a symbol of Vietnam's rich history and culture. The citadel was once the seat of the Nguyen Dynasty, and it is filled with ancient temples, palaces, and tombs. Visitors can learn about Vietnam's imperial past and enjoy the beautiful architecture and gardens. The local people are proud of their heritage and happy to share it with visitors. There are many hotels and restaurants in the area, as well as opportunities for shopping and sightseeing.

3. Ha Long Bay: This iconic bay is famous for its towering limestone cliffs, emerald waters, and picturesque islands. Visitors can take a boat tour to explore the bay, go kayaking, or hike to the top of one of the islands for panoramic views. The local people are friendly and hospitable, and there are many options for accommodation and dining, from luxury resorts to budget guesthouses.

4. Trang An Scenic Landscape Complex: This complex is another UNESCO World Heritage Site, known for its stunning natural beauty and cultural significance. It is home to many ancient temples, pagodas, and shrines, as well as beautiful rivers, lakes, and caves. Visitors can take a boat tour to explore the area, go hiking or biking, or simply enjoy the peaceful surroundings. The local people are friendly and welcoming, and there are many options for accommodation and dining.

In terms of cuisine, each of these destinations has its own unique flavors and specialties, from fresh seafood in Ha Long Bay to imperial cuisine in Hue. Visitors can also try local street food and traditional dishes, such as pho, banh mi, and bun cha. Overall, Vietnam is a wonderful destination for those seeking natural beauty, cultural richness, and warm hospitality.