Himachal is a Gem
Actually whole of Himachal has n number of treks, lakes, waterfalls in every location, so you go anywhere in Himachal you will enjoy the same and it's safe everywhere.
In tirthan valley one can go to Jibhi, serlosar lake, himalyan national park, jalori pass, chhoie waterfalls (nagini village).
Apart from tirthan valley, Parvati valley is also very beautiful and peaceful
Manikaran, hot water spring, kasol, grahan (less known) and kheergana trek, tosh, kutla(less known) are all good places to visit.
Coming down in Mandi, Parashar lake is also very blissful .