Here is the completed table:
| Holiday places | Winter or Summer? | Activities you can do there? | How often do you go there? |
|----------------|-------------------|-----------------------------|--------------------------|
| Town or city | Both | Sightseeing, shopping | Once a month |
| Mountain | Winter | Skiing, snowboarding | Once a year |
| Forest | Summer | Hiking, picnicking | Twice a year |
| Sea or lake | Summer | Swimming, boating | Once every summer |