Trekking Mt. Pinatubo (Philippines) - "Second Largest Eruption of The 20th Century"
Located on the island of Luzon, Philippines (near the provinces of Zambales, Tarlac, and Pampanga). It takes 2-3 hours bus drive from Manila to get to Mt. Pinatubo
A day tour is enough for trekking this route. You may opt for a tour company when travelling with less people with rather low price (2,000 Peso ~ $50 per person) since the travel will need multiple transportation means like bus, jeep etc.
Easy trail with rocks, sands, volcanic land structure & water streams, crater lake
Although there were a number of earthquakes around the area in July 1990, Mount Pinatubo remained its long sleep of 500 years. However, in 1991, it went exploded with climatic eruption of 35 kilometers upward. The Mount Pinatubo incident was regarded as one of the largest eruption of the 20th century, only standing after the 1912 eruption in Alaska.
Today, Mt. Pinatubo is a peaceful & worthwhile tourist spot for trekking and sightseeing not only for professionals. The location combines multiple activities in one such as riding vans and hiking. The scenery is so beautiful that I could not help myself adoring the greatness of mother nature. 
Credits:
Pictures: Self-taken
Information:
https://pubs.usgs.gov/fs/1997/fs113-97/
https://wikitravel.org/en/Mount_Pinatubo