For me personally, I'd rather go to Arenal than go to two different beach locations. Arenal has great adventure activities like Sky Trek, the big conical volcano, the waterfall hike, the Hanging Bridges, and the awesome natural hot springs like Tabacon and Eco Termales.

This is what I was thinking with my original travel plan. Everyone in my family is worried about getting tons of rain in Arenal. We are probably a little more concerned about rain than than most people since we spend a lot of our lives dealing with it in Seattle!

Any experience with Nicoya Peninsula if my parents insist?

No, we haven't been there. Technically rainy season doesn't start until May but it's not always predictable.

ABSOLUTELY!! Santa Teresa and Montezuma are amazing. Arenal is almost always in the clouds and cool. Nicoya is real Costa Rica, take the ferry from Punto Arenas (sp?) its got monkeys, beaches that are unbelieveable, rivers to swim in and not to many people. Staying at Arenal for 5 days is overkill.

We got to Arenal every year and still haven't done it all. It's really not always cool; it gets into the high 80s during the day but can cool off at night. We wear shorts and are comfortable. There's tons to do. Take a look at Tabacon and see what you think. Also Sky Trek, La Fortuna Waterfall, Cano Negro, Penas Blancas, Lake Arenal, Proyecto Asis, Rios Tropicales, and the Hanging Bridges that I mentioned. That will give you a good idea of if it's your kind of place. It's a popular place to take teens because of all the activities. Desafio and Sunset Tours have nice websites.

I think the OP said two days in Arenal not five if I'm reading it right.

Yes - our itinerary is for 2 nights in Arenal and 5 nights in MA, 3 nights at Rafiki Safari Lodge. I have a plan of what we will do if we go to Arenal. I was just trying to figure out if my parents want to switch - is Nicoya Peninsula worth the travel for 2 nights and is there stuff there to do that is different from MA?

I am pretty up to speed on all that Arenal has to offer, but I am a little nervous about possible rain and clouds (again the coming from Seattle issue).

beckybuys - do you have a lodging idea for the Montezuma/Santa Theresa area? I tried YlangYlang but they are full except their beach tents which is not going to work for us.