The Keswick Launch is a great way to take a relaxing cruise around Derwentwater.
In the summer, two ferries leave Keswick (anticlockwise 09:45, clockwise 10:00).
It has six stop offs around the lake (clockwise):
and then back to Keswick.
The round trip takes about 50 minutes, but you can hop off and on again, giving you time to explore some more.
We used it a couple of times to get us back to Keswick after a day hiking. We hopped on and off.
You can reach Keswick by road on the A66 either from j40 of the M6 or from the direction of Cockermouth.if travelling from the South Lakes,take the A591 from Windermere via Ambleside along Lake Thirlmere.
A car is an absolute must if you want to get the most out of the Lake District. Bus routes appear to be sporadic and they will not get you to some of the off the beaten path places that make the Lake District so special.
We took the train from Edinburgh to Penrith and rented a car there to drive into the Lake District. Penrith wasn't a bad place to pick up a rental car; however, there were not a lot of rental car companies to select from and it was a decent drive into Keswick and the Lake District. In retrospect, I probably would have taken the train into Cockermouth and picked a rental car up there - more selection and closer to the northern Lake District.
This is the boat landings at Keswick. From here you can take a boat to any of about 8 landings around Derwentwater. Boats leave every 15 minutes or so and alternate between heading clockwise and anticlockwise around the lake. For those used to the boats on Swiss lakes the price of short journeys on Derwentwater will be something of a shock! It's a nice way to see the lake, but an expensive mode of transport!