Between Nyköping and Norrköping, about 1.5 hours from Stockholm you will find Wreta Gestgifveri. A country-style hotel with nice rooms and access to both sauna and hot tub.
The hotel has a trendy restaurant, which can be found in the White Guide, with the motivation "A great overall experience in which the kitchen produces well-cooked meals."
I visited the accommodation during with a conference and thought the accommodation was excellent for the purpose, and I would love to go back.
A perfect place to celebrate Christmas
One of the coolest bars I have ever seen, a fireplace with a secret door
Had one of the best Christmas party ever at Wreta Gästgifveri