This is a great, 1.5 hour morning activity to start your day. The national park is located about 1 hour north of San Jose.
Poás Volcano was last active briefly in 2014, but most notably in 2009. It's one of the most active volcanos in Costa Rica. The main crater, Laguna Caliente, supports almost no aquatic life due to the incredibly high acidity.
There's a $10 entry fee into the park per person. About a quarter mile away from the parking lot lies the active Poás Volcano at 8800 feet above sea level. If you arrive before 9:30 am, you're almost guaranteed a beautiful view.
The morning we went was a wonderful mid-70 degree, clear day. We arrived at the park around 9:00 am and were pleased to see only a few other cars in the lot. The hike to the crater is 10-15 minutes of slight uphill walking; you can feel the oxygen depleting slowly, but it shouldn't be too difficult for anyone in decent shape.
We stayed at the crater outlook for about 15 minutes. It is windy, but we went in December, and it was very bearable in leggings and a light sweatshirt. The path through the forest continues to the next stop, a 20 minute hike to the very blue lagoon. The paths in the forest are cleared out well, but the footing can be a little tricky at times. Sneakers will suffice as far as footwear goes.
After 10 minutes at the lagoon, we headed back down to the parking lot, perhaps another 30 minute hike or so. There are steep inclines and declines on this portion of the path! It loops back around to the parking lot.