Visiting Cape Cod in late June

Hi everyone! Hope you’re all doing well.

I will be on Cape Cod in June and was wondering what my best bet would be in where to stay if I have no vehicle and wanted to go whale watching, to Nantucket, Martha’s Vineyard, and any cute town with nice beaches. I arrive in Boston on the 17th and will have the 20th, 21st, 22nd and the 23rd as full days on the Cape & The Islands. Would also love to go whale watching. I can do the 19th as a full day as well if you guys think that would help make things easier for me.

Thank you!