Traveling to Dublin from California for work. I have 2 days of work and then I am free. I want to see some of Ireland but have always wanted to see London. I can spend about 5 days in London after 4 days in Ireland (20 of those are work.) I know its quick- just trying to make the most of the work trip.
What are my must sees in Ireland? What is the best/most interesting way to travel from Dublin to London? What is the best part of London to stay or a woman traveling alone?
With so little time I'd suggest staying in Dublin, where there's plenty for your two free days, then flying to London (any airport), then home from there (most likely Heathrow). Maybe you'll have to return to DUB for the home flight if your company is paying for a round trip, but an "open jaw" itinerary might not cost any more.
Your must-sees depend on your interests and energy. For me in Dublin, they would include the National Archeological Museum, the General Post Office, Christ Church and St. Patrick's Cathedrals, Trinity College (including the Book of Kells), Dublin Castle, Kilmainham Gaol, and St. Stephen's Green. If you care about Irish ancestors, the EPIC center is about emigration. If you like beer or whiskey, the Guiness Storehouse and Jameson's distillery. If you want to party, Temple Bar is full of pubs and tourists. There are musical and literary pub crawls to add interest. Most of these places are within a couple of miles of each other.
Lots of places to stay in London, I doubt if you'll have a problem but I'll let the women on this forum give you the best advice. Have fun and come back for more!
"Best" is subjective.
If you can, book your flights Open Jaw meaning into Dublin and out of London you will save some time.
As for traveling between Dublin and London, you could take the ferry and then a train. This will take up the best part of a full day. Or, you can take one of the frequent flights between the two cities. It's less than 90 minutes. Assuming you have a US passport, there is no immigration traveling from Dublin to the UK. (There is the other way.)
Also be aware that if you fly back to the US from Dublin, you will go through US immigration and customs in Dublin so when you arrive in the US, it's like a domestic flight.
As for what to see, I won't recommend anything as I don't know what interests you. As for a hotel, London sites are spread out and you should be fine in most areas of central London.