Things to not miss doing in Costa Rica.

Go up to monteverde

Arenal and Manuel Antonio...been there many times and never get tired of them

White water rafting on the Rio Reventazon.

I haven't been in over 20 years so it wouldn't surprise me at all if this is no longer an option. Rent a mountain bike in La Fortuna and ride up the highway to a "water park" that backs up to Arenal volcano. Buy tickets/day pass to the water park in the morning and ride through the back of the park where there are what i've always assumed were horse trails. Follow the trails (lots of uphill, lots of pushing the bikes, crossing barbed wire, lots of mud) until the rumbling of the volcano makes you uncomfortable, then head downhill. We both times ended up on the highway a few miles farther up than where we started. Ride downhill on the highway back to the water park (where you started and bought a pass that morning). There is a swim up bar and go back in for a beer and a swim. Two different trips I've done this and it was fantastic both times. The first time the sky was clear and we watched the lava flow at darkfall from the swim up bar. One of the highlights of two different trips to CR.

Thanks might try it out. Specifically looking at the excursions we need to book way before we go is the type of things I need thoughts on.

The last time I went to Costa Rica I did an ATV excursion up/down a mountain..I don't know the name of the company but I would suggest finding someone that does something similar. It was amazing. When we got to the top there was a little restaurant tucked away that we got to eat before heading back down.

The Arenal Observatory Lodge is a great place to stay. It's got an extensive trail system, the best view of the volcano, and is off the beaten path.

In nearby La Fortuna (the town for Arenal) I can recommend Bogarin Trail. It doesn't look like much from the road but it has a good trail system and you will see sloths. And the birds are good as well, we went there for a couple of rare species and got them. And the owner is super nice. He pulled a frog out from under a banana leaf so we could get some photos.

Arenal pairs nicely with a Pacific coast spot. One place my brother really liked as a family spot was Punta Leona above Jaco.

If you drive down to the coast you can stop and see some impressive crocodiles at the Tarcoles river bridge. The mouth of the Tarcoles is a good place for Scarlet Macaws, and they are on the grounds at Punta Leona, and sometimes around Jaco too. A lot more common than they used to be.

If you're in the La Fortuna area, with the various ages in your party, Proyecto Asis is supposed to be really good and unique.

Another wildlife walk in the area that's really good is the Bogarin Trail. Two brothers who grew up in the area created a small wildlife preserve practically in the city of La Fortuna.

The Pacuare Lodge, google it.

Charter a boat out of Los Suenos resort and have it take you to isla tortuga for the day