For a company anniversary you have two main options: your own company grounds or an external venue. Both have advantages.
Celebrating at your own location creates a direct bond between guests and your company. It is also tax-attractive: events on your own grounds fall under the work-related costs scheme (WKR) and are therefore largely untaxed.
An external venue offers more possibilities in terms of capacity, technical production and wow factor. Think of an industrial building, a castle, a theatre setting or a festival site. The venue becomes part of the story.
When choosing, pay attention to accessibility, capacity and technical possibilities. The venue must also suit the concept you have in mind.