8 days...maybe a day on a beach, 2 days in Haiti, and i'll be mostly around the capital but don't mind trekking
Ok so I'm guessing you're probably staying in Punta Cana? I'll be honest, I'm not well versed on the little nooks and crannies of the Capital (I am from the North, specifically Santiago De Los Caballeros) but you should go to Mirabal Sisters Museum in Salcedo. I'm sure you know about them. About 2-3 hours from the Capital.
El Monumento de Santiago. About 3-4 hours from the Capital. It was built by Trujillo as a monument for the independence of DR from Haiti. After his death, it was dedicated to the Dominican leaders who fought against Spain for freedom. It overlooks Santiago city and yes, you can go to the top (of course, if it's open that day). In the daytime, wonderful tourist-y spot. Learn history, ride a horse-drawn carriage, have lunch at one of the 1000 restaurants across the street or buy street food.
In the night tho
get wasted, debauchery, loud music, motorcycle/car racing, find good weed, cars crowding the street blasting music with their loudest speakers, loads of bars/clubs. Nightlife
The thing about this area of DR is that there are A LOT of little museums if you walk around. Especially in la Calle Del Sol which is like main street. Bunch of shops, museums, general information kiosks, etc.
My cousin's mother is from the South/Capital area. I can ask her the best tourist-y museum places there aside from La Zona Colonial which is the most obvious. I'll get back to you.