A very good way to go on an unforgettable trip of a lifetime and make a lasting impact is to volunteer your services.
There are several websites that are dedicated to senior volunteer travel. Do a quick internet search to find them. Some require a low daily fee. Several offer home-stays, dormitory stays, airport pick-up, meals, etc. Also, several mention solo travelers specifically.
Another way to volunteer is with your church if you are so inclined. I’ve attended several garage sales benefiting missions.