The markets are great in the evening; and they will be pretty close to where your boat is docked. If not close then just down the river and accessible on the 2 Tram. A few boats do park on the Buda side but not many. If thats your situation then its a bit trickier.
For a day in Budapest it all depends on your interests. There is the market hall, Jewish/holocaust Budapest, WWII Budapest, Soviet Occupation Budapest, Art Nouveau Budapest, theater, classical concerts, jazz clubs, food, museums; or you can do the standard tour.
Hotel to 4/6 tram one stop towards the river https://goo.gl/maps/Aam5sjsLtTs
walk up Falk Miska utca and visit the antique shops
Continue to the Parliament and be there at 9:15 https://goo.gl/maps/T4jpoX6Wkj42
9:45 am Parliament tour (book in advance on line) http://latogatokozpont.parlament.hu/en
hop on the 2 Tram and ride it to the Great Market Hall (long beautiful journey) https://goo.gl/maps/rgvb7NE8KdL2
11 am unitl 12:30, the Great Market Hall - tour the basement, ground and first floors; shop for junk upstairs.
47/49 tram to Great (Dohany) Synagogue, arrive about 12:45 and take the short tour that starts on the hour. https://goo.gl/maps/ZZTTCEUnHs92
Walk up Dob utca to http://www.spinozahaz.hu/ for lunch
Back down Dob utca one block to Rumbach utca, then down Rumbach utca to Kiraly utca (you can short cut through the Gozsdu udvar if you want)
Walk up Kiraly utca to Vasvari Pal utca. If it's 3pm or later, stop for a glass of wine at Kadarka, if its before 3 pm buy a pastry at the shop on Kiraly utca just beyond Kadarka.
Now down Vasvari Pal utca to the Opera House. https://goo.gl/maps/qT2smc11JMk
Should be about 3 pm by now.
Walk to Oktogon ter
Take M1 metro up 2 stops get out and walk up Andrassy ut past the mansions for a stop or two.
Back on metro to Hero's square
Walk to the Bath House and party till 7pm https://goo.gl/maps/uS7ZooeUiv22 (the map shows the metro line, but the metro runs directly under Andrassy ut with numerous stops so you can get on and off and see some of the architecture along the way.
Return to Hero's square on the M1 and Walk to http://www.paprikavendeglo.hu/ for dinner https://goo.gl/maps/3fhYuVwzGYp
Return to Hero's square and the M1 to the Oktogon for more play or to Deak Ferenc ter for the transfer to the M3 and home.
Its about an hour of walking in-between trams and metro line.... Don't be skiddish about the metro line. Its the M1 and its the oldest underground on the continent of Europe which makes it sort of a historic sight all of its own. Very easy to navigate.