For in-person summer math experiences, there is https://rossprogram.org/ https://rossprogram.org/ among other math camps many of which are listed at https://sum

For in-person summer math experiences, there is https://rossprogram.org/ https://rossprogram.org/ among other math camps many of which are listed at https://summermathprograms.org/ https://summermathprograms.org/ Ross provides significant need-based financial aid (which can cover all fees for the six-week program).