I had a great time being a member of the team (organization name). It was a fantastic experience, and I was able to hone my skills while learning a few new ones. I'd want to thank my instructors (tag them) for twisting and pulling my thoughts in unexpected directions while encouraging me to find the answers I needed.
Thank you so much for giving me the chance to work as your [internship title]. Without your [continuous feedback/support/guidance/mentorship], I am convinced that I would not have progressed and learned as much as I have in the last [X weeks/months]. I'm grateful for [their advice or experience], and I especially appreciated [your favourite endeavour or opportunity].
I'm more excited than ever to pursue a career in [area] as a result of this experience, and I feel well-equipped to take on [position or responsibility you'd like to take on]. I'd like to keep in touch as I [complete school/change careers/go through another transition]. You can contact me via email or phone at [email address]. And I hope you'll let me know if there are any openings in your department down the road so I can apply.
Thank you again for this fantastic internship, and I wish you and the [team] the best of luck in the future.
[Your Full Name]
I wanted to thank you for being a wonderful [teammate/mentor] and support network on the last day of my internship. I've truly loved [your experience together] and can't wait to apply [what you learned from them] to my new career. I'll remember [some amazing experience you had together] in particular.
While I won't be in the office any longer, I'd want to keep in touch and perhaps meet up for coffee the next time I'm in town.
Best of luck to you and the rest of the [team]!
Thank you once more,
[Your Full Name]