Agree on the Hafod estate, I came across it by accident earlier this year when taking the scenic route home from Aberystwyth to Bristol via the Elan valley.
The Doethie valley from Llyn Brianne to Ty'n-y-cornel hostel is a cracking walking with an overnight at the simple hostel in a remote area with no mobile signal a real get away from it all.
Also in south Wales the walks around Cwm Carn forest park including Twmbarlwm are very nice.
Finally the Gordano Round
https://www.ldwa.org.uk/ldp/members/show_publication.php?publication_id=2452which is a figure of 8 so split into two separate 14 mile ish days out takes in some nice paths between Portishead and Clevedon, it's a good one for me if I can't be bothered to drive to far.
Too many choices, not enough weekends...