Make these basic decisions at an early stage, because handling travel arrangements and accommodation is time-consuming and ultimately often a thankless task (changes to bookings, cancellations). There are always options for outsourcing this work.
Many organisers just invite delegates to the event itself and leave travel and accommodation to them. However, there is a list of hotel partners who offer special prices within certain booking periods which may help you. Some offer packages that include a minimum of specific accommodation and others act as travel agencies and take care of everything from rail/air tickets to all transfers and accommodation. The larger the number of participants, the more problematic the logistics.
You are recommended to engage the services of a local destination management company (DMC). Some municipal authorities support events by offering free or discounted public transport tickets. Local tourist offices may also sponsor cards providing cut-price admission to museums etc.
Tip: Make use of third party logistics and software.
If you don't have your own travel department, you might want to try Lufthansa Meetings & Events – your travel solution. Perhaps you'd rather keep your carbon emissions down and travel overland, in which case Deutsche Bahn's event ticket could be the solution.