The zoo? Why would you go to the zoo? Ditto the botanical gardens, I am sure they have plants where you are. And March not the best month for plants to be blooming. I would not pay £10 to see a military barracks. Then again, I have. I think there may be a fiddle festival in March.
Tradfest is in April, fiddle festival in November, although you can hear trad musicians any night at Sandy Bell's.
All good zoos have their different strong points - Edinburgh is known for its penguins, its monkey house and its giant pandas. It's also one of the few places in Europe where you can see koalas.

And after Sandy Bells closes, the Royal Oak! One time I was there the small upstairs bar had several Americans (it must be in a guide book), one of whom was bewailing the talent on offer. She should have stuck around till later, when everyone who could negotiate the stairs was downstairs.
That was in my late youth/early middle age though. Long time ago.
Pretty hard to get musicians up to speed before 11pm. They generally hit their stride about closing time.
last trip to Edinburgh we went and saw the Royal Yacht Britannia - I thought it was worth the visit.
Agree with RayC - hop on hop off bus - the history lesson which goes with the commentary is always interesting and informative.
Done it several times Poppy, and would do it again.
Not the Britannia, but my wife would.
A coffee or a plate of soup at The Dome in George St is also a must for us out-of-towners, if only to gawp at the amazing ornate interiors. They do a good haggis and neeps too, if you want to try some.
Nearby back-to-back pubs Café Royal and the Guildford Arms also have beautiful interiors and good real ale.
rayc - do them in each town I visit. Did the London one again last year, sat downstairs saw a different view of things. Catching public transport buses isn't quite the same.