Well, at this time of year your outdoor options are limited unless you're happy being out in any weather, but any of:
(Indoor) Climbing, ninja warrior (indoor assault course/soft play for adults), museums, art galleries, theatre, comedy, gig (pub or otherwise), quiz night, movie, bowling, pool/snooker, board game café, city-wide treasure hunt, ghost walk or history walk, ruins/castles/stately homes/Roman villas, some kind of taster/one-off class or workshop (e.g. pottery, photography, dancing, acting, crafts, making, unusual sports taster, such as fencing etc), a car or bike track day, day at an archery range or shooting range, caving, indoor skydiving, old-fashioned steam railway, murder mystery evening, day being an animal keeper at a zoo, outdoor sculpture park, sushi or cocktail making, butchery day, wine/beer/gin/whisky tasting, cheese tasting, air soft / paintball, tank driving, forestry/outdoor/survival skills days.
Loads more options in the summer, as well, if you're planning for the future?