Mulshi, Alibaug, Lavasa, Aamby Valley, Matheran are some of the options. (Lots of Airbnbs here).
There is Adlabs Imagica if you want to do a adventure/theme park kind of thing.
If you go to Nashik side (~5h drive), there are vineyards with places to stay as well (I think Sula has accommodation).
Goa is about 8h drive (might be worth it for a 4-5 day trip) as well.