you only need a story to make an adventure. with that in mind, any module from any edition can be directly (more or less) converted to 5th edition. all you have to do is substitute the 5th edition version of the monster. in the cases where an early edition monster is too strong or not strong enough, this is a brilliant and useful encounter building tool:
http://asmor.com/5e/monsters/#/encounter-builder
in some cases you will have a monster that doesnt have a 5E stat block. you can sub in a similar monster to fix this: giant lizards and ambush drakes are almost identical; different spiders can be subbed by Giant Spider (or if youre creative, use that as a template to convert the phase spider, sword spider, or whatever).
long story short, you can easily come up with thousands of hours of playable material with some easy conversion work.