Hi Swati, Vietnam is great place to be explored solo. If you have few days you can cover Saigon, Hoi An, Hanoi, Ha long Bay. You can find details about my solo trip to Vietnam here: https://goo.gl/gXKLpF Keep exploring!
Hello Swati, I visited Vietnam this July and it was awesome. You can go to Hanoi and stay @backpacker area from where you can go to cat ba islands(avoid ha long bay area as it crowded and similar nature can be witnessed @Catba island) its great. Post that, you can go travel to Sapa(nature @its best) again via Hanoi. you can catch a train(good experience) or flight to Ho Chi Minh City(Saigon). In Saigon, u'l mostly find Vietnam War museums and places relevant to it (nothing else). Aprt from that you can explore Mekong Delta (2 days are enough) and Nha Trang 450kms away. Thats it and PEOPLE are awesome and make you feel good and homely :) Good Luck!!