I visited kasol this year.
Kasol is a small town.
You can spend a day in Kasol where you can trek besides river and camp besides parvati river.
Visit Manikaran Gurudwara and hot springs at manikaran.
Visit Tosh village. It has some amazing cafes and beautiful views like 360 degree cafe.
You can also visit kalga and puga village and stay over there.
Visit kheerganga by trekking. There are hot springs on the top. Trek up.
There is also a trek for mana village on the other side of kasol.
Buses and taxis are easily available in Kasol.
Hey Sid, Add Malana in your itinerary. It is such a good village with the oldest democracy. You can visit Rasol. it is also nearby.
You can visit Tosh, Pulga, and Kutla. All these places are very pleasing.
And yes don't forget to visit Manikaran Gurudwara. Manikaran is very near to Kasol and you will experience Hot Springs there where the rice and veggies are boiled in the natural hot water :D
Kheerganga trek starts from kalga. it needs 7 hours up to down. see my trip vlog for details. tosh is nice place you can visit . if want trek to kutla village it will be a best choice to go. its 3 hour trek chalal village is nice but its just a,waste of time. you can,go kalga n pulga its walking distance near Bharsaini for more detail info messge me on insta @harsh_singhaao
Kheerganga in the above 2 or ditch both and go to Chitkul...n stay in some homestay njy local food and treks.... beautiful place.it takes 5-6 hours from shimla to reach there.u can either take a cab or local bus to reach there. as a solo traveller prefer bus.