The National Trust is to reopen some gardens and parklands in England and Northern Ireland from 3 June.
Around 29 sites are due to open to those with pre-booked tickets, with more to follow in the coming weeks.
Only around a third of the usual number of visitors will be permitted in order to maintain social distancing.
It comes after the PM announced a further easing of lockdown measures in England, while Northern Ireland has moved to reopen outdoor spaces.
All properties and car parks in Wales will remain closed, however, in line with Welsh lockdown rules.
Belton House in Lincolnshire, Cliveden in Buckinghamshire and Mottisfont in Hampshire are among the sites where visits to outdoor spaces can now be booked in advance.
However, facilities at its sites - including houses, shops, holiday cottages, and campsites - will all remain closed.
The Trust said most coastal and countryside car parks are already open, but some busier ones may need to be closed or pre-booked.
Hilary McGrady, the Trust's director general, said the aim was to reopen gardens and parks "wherever possible".
But she cautioned that "things will be very different, particularly at first".
The Royal Horticultural Society (RHS) is also reopening its four gardens around England with a pre-booked ticketing system on 1 June.