The Sendero Arenal 1968 is a great setting for a relatively short hike through the lava rocks dating to the eruption of the Arenal Volcano in July 1968, and it makes for a great half day excursion. The walk through the forest and rocky terrain offers opportunities to see many bird and insect species, and in clear days, great views of the volcano. A guide is not required, as the trail is well marked, though a knowledgeable guide can help you learn about the local fauna, flora and history.
The location is in a private property, located about half an hour drive from La Fortuna, and requires a $10 entrance fee. It is adjacent to the Arenal Volcano National Park. There is a large parking lot at the trailhead, where you can also find clear restrooms. A short walk leads to a view point of the volcano, where there is also a cafe (or "fuente de soda," as locals call small roadside restaurants and cafes).
The first two-thirds of a mile are mostly flat, offering great views of the vocano as well as some of the local crops grown in the property, including plantains and sugar cane. After that the hike ascends through the forest, over volcanic rocks left by the eruption. Before the 1968 eruption, villagers around the mountain did not know it was actually a volcano. Unfortunately, dozens of people perished as a result of the eruption, which sent lava, rocks, ashes and fumes hundreds of feet in the air, and miles away from the volcano. One mile of this hike is on volcanic rock, which is slowly being taken over by the forest.
As you ascend, make sure to look back (away from the volcano), for great views of Arenal Lake. This was a natural lake, which was significantly enlarged through the construction of a dam, thus displacing small villages in the area. After 1.2 miles, the trail reaches its highest point, which is some 300 feet higher than the trailhead. That is still a few miles away from the crater, which is off limits for safety reasons.
The last half-mile makes for a very pleasant walk where you can observe colorful birds and butterflies. As the trail is quite rocky at times, sturdy shoes are recommended, along with insect repellent, sunscreen and a hat.
After this hike, you may enjoy some of the nice hot springs resorts near the park, on the way back to La Fortuna.