Drier beach areas in September would be on the Caribbean side - check out Puerto Viejo, Cahuita, Playa Negra, Cocles, Manzanillo areas.

With five nights I would definitely only do one area. Distances are far and you'd spend too much time on the road. Depending on your arrival and departure flights you may have to overnight near the airport which cuts your time even more.

I think you need to make a choice as to whether you want beach or volcano/hot springs, but with this short of a trip, I would not do both.

Most of the hotels on the southern Caribbean coast are smaller, locally owned lodges - no megaresorts here. You can go whitewater rafting, hiking, snorkeling, go to jaguar and sloth rescue centers and visit indigenous reserves.

Arenal is one of the top tourist destinations and you'll find more adventure activities here such as ziplining, canyoneering, rafting along with thermal springs, hanging bridges, waterfall hikes and Cano Negro boat trip.

Interbus and Grayline both offer public shuttles, plus you can do a search on this forum for a list of private drivers.

Have a great trip!

Thank you for the great insight!

Two Great areas in Costa Rica are La Fortuna and Nicoya Peninsula.
La Fortuna is great, full of adventure and nature. it is really close to Arenal . Whitewater rafting and kayaking, Canopy , Rappel , Horseback ridding , mountain Bike and much more adventure.

Nicoya Peninsula: Long roat , but an unimaginable place. Many great Beach , Mal Pais, Nosara, Santa Teresa etc. wildlife refuges. Great place to Surf , if you do know surf, do not worry you will learn as soon as you want.

September is one of the rainiest months of the year on the west side and in the mountains of Costa Rica. The Pacific beaches and central region get significant rain most days; generally with a pattern of sunny mornings followed by showers in the afternoon or evening. Occasionally tropical lows stall off west coast or the edge of a hurricane skims across from the Caribbean bringing several days of continuous heavy rains.

In August 2004 we went to Costa Rica & the weather wasn't bad at all. I would do it again if that was the only time of year we could go. It was sunny every day except it would rain like clockwork around 4PM for 30 minutes. Not sure if it would be the same in September. But the weather didn't stop us from doing everything we wanted to do. We were there for 10 days & divided our trip between Manuel Antonio, Arenal, Poas & Alajuela near San Jose.

Forgot to add that we rented a car because we like the freedom of driving ourselves & making our own schedule. My husband & daughter shared the driving. We did not drive over the mountains at night. The signage in 2004 wasn't great in some areas, so we made some wrong turns but figured it out & had some laughs.

You best bet would be the Caribbean side. The end of Sept towards Oct is getting to be THE Green Season on the West side of the mountains. You can't tell until the time comes as it can rain anytime or it could just be afternoon showers. But, for the best chance of dry, it would be on the East side. If you are up to renting a car, wait until the day before or the morning of and if it looks like good weather, take a day trip out & about.

Two Great areas in Costa Rica are La Fortuna and Nicoya Peninsula.
La Fortuna is great, full of adventure and nature.