There are a number of ways to get from the UK to the Baltic, but unless you want to go round the top of Denmark, they all involve going through the Kiel Canal.
Its actually possible to day sail all the way from the UK, and many people do. Its almost possible to travel there without going out to sea.
The only significant hazard on the way to Kiel is the Elbe Estuary. This is notorious in strong winds and merits some respect, otherwise the trip is straightforward.
The most direct route for people coming from the East of England is a direct hop across the North Sea from Felixstowe or Harwich to Ijmuden. This leg, which takes about 22-24 hours, steers clear of the TSS near Rotterdam and has only the deep water route (which it crosses at right angles) and the gas fields to contend with.
For yachts coming from the south coast who do not want to cross the Thames Estuary, you can coast hop along the Belgian Coast to Vlissingen in the southern Netherlands. From here you can either travel north along the (rather windswept) Dutch coast, doing your best to miss the mas of shipping around Rotterdam, or you can take the pretty but time consuming inland route through the Dutch canals and lakes up to Amsterdam.
From Ijmuden or Amsterdam, once again you can either travel up the coast to Den Helder and along the northen coast of the Frisian Islands, or you can take an inland route through the Ijsselmeer. There is a mast-up route all the way from Amsterdam to Delfzil on the Ems. A short trip down that river brings you to Borkum and out into the North Sea.
The Frisian Islands have few ports of refuge, and those that do have awkward entrances, but a good jumping off point for the Elbe is Norderney. From here it is only 63 miles to Cuxhaven.
From Cuxhaven, a short trip up the Elbe takes you to Bunsbuttel and the entrance to the Kiel Canal.
There is one more option - travelling inside the Frisian Islands. This however is an advanced topic. Its only suitable for those with shallow draft, and not of a nervous disposition.
The following pages cover these routes and stopping places in some more detail.