I visited the Powis Castle with friends yesterday - and we had a wonderful time.
Ample parking. Very well signposted from Welshpool.
A beautiful place, both inside and out. The museum and castle, were full of beautiful rooms with oak paneling, ornate ceilings, lovely furniture and other interesting exhibits. Very knowledgeable and friendly staff. Wonderful views through the windows!
The cafe was nice. A little overpriced ... but not that bad really. Tea for three was just under £5, to give you an idea.
The gardens are wonderful - although the rain prevented us from conducting a full exploration.
Just three points - which didn't affect me, but may concern others ....
No dogs are allowed, apart from guide dogs ... even in the gardens.
As with most places like this, photography is not allowed inside - and mobiles must be turned off (inside) - even if on 'silent'.
The entrance fee is a little steep if you're not a National Trust member. The standard adult fee (for the castle and grounds) is £11.80, but they 'push' the Gift Aided option of £13.00, which includes a voluntary donation. There are cheaper options - such as castle only - or grounds only. I didn't take note of these prices, as we wanted to experience everything. There is also a family entrance fee - which again, I didn't take note of. (Details are on their website).
All in all - highly recommended!