Trsteno
is 30 km far from
Dubrovnik. It is known for “Arboretum Trsteno”, a magnificent
botanic
garden, started 500 years ago by family Gučetić, is planted
in wonderful Mediterranean surrounding. Multiple daily guided
trips are organized from Dubrovnik, but they are very short and I would
recommend to come on your own and spend a half a day in solitude and
tranquility.
Make sure that you have enough films (or storage media).
See more here.