Saga have an arrangement with Hilton where you can get good rates for nights and mini breaks.
The mini breaks also include "free" dinner on the first night.
Many Hilton Hotels have a swimming pool and other amenities on site.
Note that Saga is an organization aimed at the over 50s, so to take advantage of this deal you must be over 50.
I have no idea how strictly this is enforced (it certainly isn't at time of booking) and it has never been checked when I have arrived at the hotel. If someone was obviously under 50 I am not sure if the Hilton would ask for proof of age.
Saga web site for booking http://www.saga.co.uk/hilton
Hilton UK web sitehttp://www.hilton.co.uk/