been years since i last went to the dungeons so might have improved but i remember it was pretty brief.. in and out in 1/2 hr
museum gardens are nice if weather is good, cliffords tower always an option.
If you like big country estates then you have Beningborough Hall out towards Newton on Ouse, about a 20 minute drive up the A19, its a national trust property lovely gardens and then you can stop off at the Dawnay Arms in Newton for a spot of lunch, nice beer garden by the river and good scram
your also not far from Linton-on-Ouse RAF base if your into planes