Spring and summer offer the best weather for outdoor exploration. Weekday mornings are generally less crowded for the museum.
The best time to visit Old Assen Castle and its surrounding gardens (the Abbey Garden) is during spring (April-May) and summer (June-August). During these seasons, the weather is most favorable for walking around the grounds, and the gardens are in full bloom, enhancing the visual appeal. Autumn (September-October) can also be picturesque with changing foliage.
For visiting the Drents Museum, which is part of the complex, weekday mornings, shortly after opening, are generally the least crowded times. This allows for a more relaxed experience of the exhibitions. Weekends and school holidays typically see higher visitor numbers. Checking the museum's opening hours and any special event schedules beforehand is advisable.