Some ideas to make a Birthday Trip-Gift last a long time.
For your sense of confidence, take a trip that has a little sizzle: a boat on the Ganges? an elephant ride in Northern Thailand? a walk through a Dowry Market in Pushkar? a visit to a poignant museum about apartheid?
For introspection: travel solo but in a group. You will learn new dynamics away from friends and away from home. You will also concentrate on yourself for a change.
For health: swear off all sugars and alcohol during the trip. That will be easy if you choose a place not known for wine and ice cream! China or other Asian destinations ? PS You will also feel better and have less jet lag.
For your brain: read ahead of time. A good tour company will supply a list of books to help you prepare for your trip. Books can be heavy duty histories or fun travelogues starring women. Some women writers to try: Dervla Murphy, Mary Lee Settle, Mary Beth Bond, Freya Stark.
For new insighfulness: choose a place outside of the US, with a different language and different customs. Watch how people communicate, read the English language newspaper of the area on line for a sense of what is really going on.
For your body: learn discipline and pack lightly with monotone clothes, scarves and only 2 pairs of shoes: one for walking and one for looking.