Dublin is very walkable. You mentioned liking beer and culture, obviously the Guinness tour has both, but it's hardly a killer insight!
Given you have four days, spending at least one of them outside Dublin may be of interest. A day trip to Glendalough is well worth it - it is beautiful there. Anther option would be taking the train up to Belfast (very reasonably priced and a comfortable journey) - again, very walkable and I can't speak highly enough of visiting the Titanic Exhibition - it is one of the best tourist attractions I've ever visited.
https://www.titanicbelfast.com/explore/.
In London, I'd advise against hotel breakfasts - generally they are overpriced and bland - there are countless better options no matter where you're staying in London. For a short economical and a great viewing experience, I recommend going on the London
https://londoncablecar.ventrata.site...iAAEgInE_D_BwE. But don't bother with any of the packages, just walk up and get a return or one way ticket. If doing one way, I recommend taking the DLR to Royal Victoria Docks and taking the cable car to the O2 arena where there are lots of shops and restaurants.
Enjoy!