Sample 1-
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.
Sample 2-
Hello, [Name],
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.
Warmly,
[Your Full Name]