* The 259-room Inn at Penn, the hospitality component of the University of Pennsylvania's new mixed-use complex, Sansom Common, will open in 1999. The property will include a conference center with a ballroom, eight meeting rooms, and a 16-seat fixed boardroom.

* The 526-room Westin Hotel at the Denver International Airport will open in the summer of 2001. The full-service hotel will be atop a 1,400-space parking garage and will have 30,000 square feet of meeting space, a health club, and a business center. It was designed with the capability of being expanded to 1,000 rooms.

* The 424-room Four Seasons Hotel Las Vegas is billing itself as an oasis of tranquility in bustling Vegas. The hotel will be part of Mandalay Bay Resort & Casino, a new 60-acre resort and entertainment complex. When it opens early next year, the Four Seasons, a nongaming hotel, will feature an 11,000-square-foot main ballroom with a 4,000-square-foot prefunction space, a 6,000-square-foot junior ballroom with 2,300 square feet of prefunction space, plus five smaller conference rooms, a health club, and a business center.

* The newly opened New York Marriott Brooklyn is Brooklyn's first new hotel construction in 68 years. Part of a mixed-use development, the 376-room hotel has 27,000 square feet of meeting space, including an 18,000-square-foot grand ballroom.

* The 197-room Club Hotel by Double-tree at Bayside in Boston will open in April next to the Bayside Expo and Conference Center. Bayside Expo has 270,000 square feet of exhibit space and 30,000 square feet of meeting space. An additional 18,000 square feet of space encompassing 10 new meeting rooms and a ballroom will open at the end of this year adjacent to the hotel.

Renovations, Renamings * International Conference Resorts has been named to manage the Carefree Conference Resort in Carefree, Ariz. A $10 million renovation and expansion of the property is under way. The 10,000-square-foot Saguaro meeting room, the Mesquite Dining Room, a media and business center, and 62 guest rooms are being added. Two new special event venues--the 8,000-square-foot Carefree Opera House with a U-shaped, 3,000-square-foot balcony; and The Saloon, with indoor and outdoor bars--also expand the group options. The project, set for completion this fall, brings accommodations at the resort to 248 rooms, suites, and casitas.

* International Conference Resorts also recently was named to manage the Ocean Place Hilton Resort on Ocean Boulevard in Long Branch, N.J. The 254-room resort offers 35,500 square feet of meeting space.

* The Radisson Hotel Atlanta is undergoing a $24 million renovation by its new owner, Amerimar Enterprises, who will rename it the Spirit of Atlanta Hotel. It is set for completion next spring.

* Beginning this year, the Arnold and Mabel Beckman Center of the National Academies of Sciences and Engineering, in Irvine, Calif., has been open to the business community at large. Since its opening in April 1988, the conference center had been reserved for use by the National Academies of Sciences and Engineering, the Institute of Medicine, the National Research Council, and other select nonprofit organizations. Located next to the University of California, Irvine, the 48,000-square-foot facility offers a 250-seat auditorium, a lecture room, and several conference rooms, as well as food service and technical support.

* Pfizer Inc. has signed a 15-year lease for the $35 million Corporate Learning and Development Center at the Doral Arrow-wood in Rye Brook, N.Y. Pfizer will conduct its worldwide training at the new facility, to be developed by Doral Hotels and Resorts. The center will have 110,000 square feet of meeting space, and 100 guest rooms will be added to the Doral Arrow-wood to accommodate Pfizer's estimated 33,000 room nights per year.