Time to kill around Ho Chi Minh City

Hello everyone, Me and my wife just spend 5 days in HCMC and we have a volunteering starting in the 29 of May near Cat Tien National Parc, and we were wondering where to spend this 5/6 days spare ? HCMC is cool but we visited everything interesting and we crave for some nature and cute place. Is it a place you would recommand not too far so we can still easily go at our volunteering soon ? I heard about Mũi Né, seems cool but a bit far. Thank you!