This particular scenario can be played as an addition to your current adventure when players are traveling or played as a short session. The following D&D adventure can be inserted into any campaign in which characters travel through wilderness areas. The adventure can also be played as a short session. It is best suited for 1-4 characters of 1st-3rd level, though it can be used as a side trip for most any level to relieve the boredom of a journey through the wilderness.
The adventure starts as the party is traveling off-road through forested hills in the early afternoon. The Dungeon Master should read the boxed text to the players or paraphrase it as desired.
With a little imagination, converting to DnD 5e, Pathfinder, etc. should be very easy for any Dungeon Master, but if you need help on conversion to 5e, I created this page for such an occasion: Convert Old Dungeons and Dragons Adventures To 5e