Appearing before a few reporters, including PEOPLE, Princess Diana's brother, Charles Spencer, 38, on Wednesday posed with his wife of six months, Caroline, 34, and said she was his "best acquisition" he had made. Clearly still reveling in the glow of post-wedding bliss, the couple, basking in the summer sunshine at Diana's ancestral home, Althorp, revealed that they are already planning a second honeymoon -- taking a drive in an open-topped car from San Francisco to Yosemite National Park. "It will be wonderful," she said. "Just the two of us and very romantic." First, however, comes the opening of Spencer's estate and Diana museum to the public on July 1 (which would have been Diana's 41st birthday). This year, the public can view Diana's island burial site and exhibits for an extra month as Spencer plans to keep the estate open through the end of September. But it will be closed on what will be the fifth anniversary of the princess's death, Aug. 31. Spencer has also added a nature trail to entertain youngsters who are likely to be bored with traipsing around the 500-year-old home. He told PEOPLE that his four children, who are back from Cape Town, South Africa, where they live with Spencer's first wife, Victoria, will be the "guinea pigs" to test out the trail this weekend. Meanwhile, he told PEOPLE that the extended stepfamily (Caroline has two boys from her marriage to PR guru Matthew Freud) "gets on well, which is great because you never know in these situations. It's a bit like 'The Brady Bunch' -- three girls and three boys."