Taking a steamer trip on Ullswater is a "must see" (or "must do") activity in its own right, but it's also a way to get here - provided you want to get here from Howtown or Pooley Bridge, the only two other stops on the lake.
The views from the boats are fantastic and the two "vintage" boats "Lady" and "Raven" are superb ("Raven" is my favourite). The woodwork and the brass is lovely and the interior saloon is quite splendid, though I prefer to spend my trip out on deck.
Fares are not especially cheap - the shortest journey is Glenridding to Howtown, taking about 1/2 hour and costing 3.90 pounds one way.
Busses do come to Glenridding, there are services here from Keswick, Penrith and Windermere, though these number only about 5 trips per day on each route. Check carefully the times of the busses to avoid getting stuck here!
Many people come to Glenridding by car and at the height of summer it can be a real pain to get parked here, unless you arrive quite early. There are large car parks by the tourist information centre and the steamer landings and if you can't get into these you'll have to drive further up to Patterdale and walk back (15 minutes walk).