I drove myself there, and it must be said that the roads that lead to La Fortuna (the closest decent sized town to the volcano) are very dark, and on the cool December night I arrived, they were very foggy too. A little scary at times, particularly as the local trucks coming the other direction never slow down as they pass. Being in near total darkness, with fog limiting visibility and having trucks pass by about a foot to your left is definitely a rather hair raising experience. If you do choose to drive, try and arrive in daylight, and please be extra careful.
Most visitors use La Fortuna as their base, and though it's a convenient option, the town itself is little more than an unremarkable collection of hotels, restaurants and stores. It is the closest real town to the volcano, however, and is your best bet for finding a tour or booking a guide. Arenal is one of Costa Rica's top tourist sites, so you'll be able to find a trip here from just about every part of the country. I would recommend coming for at least two days; the volcano itself is often hidden behind clouds, and it's not uncommon for people to come here and never get to see the thing.
An alternative to La Fortuna, and one that I would recommend from personal experience, is the Arenal Observatory Lodge a few miles down the road. It was originally a Smithsonian research facility, and is the closet accommodation to the volcano itself. Its extraordinary location, just 1.7 miles from the volcano, means it still attracts researchers from all over the world. A Four Seasons it is not, but who needs that sort of pampered luxury when you're so close to an active volcano? If you like unique one-of-a-kind experiences, you should stay here. If you're more of a five-star resort kind of vacationer, then there's plenty of spots like that between the lodge and La Fortuna.
And speaking of the volcano...the lodge has a fantastic viewing deck, with chairs set up for you to stake out the summit. I was really lucky: my first morning, as the clouds parted almost immediately and offered up a crystal clear view of the crater. What I saw literally took my breath away; it's one of those moments that will stay with me forever. Just wonderful.
Later that afternoon, thick clouds arrived in the blink of an eye and the visibility was again shot. If this happens to you (or even if it doesn't), I highly recommend a trip down to the lake. There are frequent boat tours from here, and even when the weather is bad, it is an amazing, beautiful and utterly unique experience. I actually enjoyed driving around the lake, and the brooding atmospheric feeling it evoked, just as much as the volcano.
If you do go visit, don't be too disappointed if the clouds obscure your view. There's plenty to love about this place irrespective of the visibility, you just have to search it out.
[Photos: Kai MacMahon]