Costa Rica hiking
The Arenal area is beautiful in April, though it's a chancy thing to see the volcano activity because of the frequent cloud cover. One nice hike, from the area of the Arenal Observatory or just beyond it on the observatory road, is to the smaller and inactive sister peak just to the west. I forget the name but it's in the guidebooks. Agree with previous poster that the Monteverde area is a good stop, lots of walks there in the cloud forest. Also, if you're adventourous, you can hike from the Monteverde/St. Helena area down to the southern tip of Lago Arenal but as with almost any distance hiking in Costa Rica, be forwarned that the trails aren't exactly marked with AMC-type signs. In Costa Rica, even houses and businesses don't have "addresses" as we know them, which of course only adds to the adventure. Costa Rica is a beautiful country with wonderful people. Hoping you enjoy it!
John