The most convenient way is by car. If you're using public transit, check out the trip planner on http://www.511.org.
It is also easy to get around by bike or by walking. Lots of good destinations. There are two downtown shopping areas: the primary downtown is between 2nd and 5th streets, bordered by El Camino Real and the train tracks. The big, new San Mateo Public Library is also downtown. The "other" downtown is south about 15 blocks, at 25th ave on the West side of El Camino Real. Continuing south on El Camino Real is the Hillsdale Mall.
Central Park is located off of El Camino Real between 5th Ave and 9th Ave. Inside the park is a beautiful Japanese Tea Garden. There is also a small train on rails for children that runs for a few hours each weekend day all year round and during the week during the summer.
North of the park, downtown San Mateo runs along 3rd Avenue and 4th Avenue (spilling somewhat onto 2nd Avenue) between El Camino Real and the Caltrain train tracks; it's one of the more successful urban downtowns left on the Peninsula. The streets with the most restaurants and other establishments are B Street, 3rd Avenue, 4th Avenue and 2nd Avenue.
Until recently, San Mateo was home to the only horse racing track on the San Francisco Peninsula, Bay Meadows. It's being redeveloped, although the structure is (as of mid-2010) still visible from the outside. The grounds are also home to the San Mateo County Events Center, where the annual county fair is held and various other events (including the recent Bay Area stops of Maker Faire. Take the Delaware Street exit off of Highway 92 and head south; the Event Center parking lot is directly off Delaware. What part of Bay Meadows remains visible are best viewed on foot from this area.
For fans of the local mid-century modern architecture, San Mateo is home to two Eichler neighborhoods - 19th Avenue park is a very early tract group of Eichlers, and The Highlands is a later neighborhood of custom Eichlers.
Coyote Point is a park located in the North-East corner of San Mateo off of Highway 101 at Peninsula Avenue. A small boat harbor is there as well as a natural history museum. There is also a public shooting range, open weekday evenings.
Poplar Creek golf course, a municipal course, is located there as well. A hiking trail allows easy access to San Francisco Bay.
Crystal Springs Reservoir is located in the watershed area off of Highway 280 on the western edge of San Mateo. Crystal Springs dam is located just south of Crystal Springs off of Skyline Boulevard.
M is for Mystery, 86 East Third Avenue, (650) 401-8077 An excellent mystery bookstore, with knowledgable staff. Holds many readings.
Hillsdale Mall. A large enclosed mall with mid- to high-end shops. Features Macy's, Nordstrom, Sears.
The area of downtown San Mateo around the intersection of 3rd Avenue and B street has a large number of local shops. There are also smaller shopping streets around 25th Avenue and 41st avenue, in both cases just west of El Camino Real.
Thai Satay, 173 E 4th Avenue, (650) 342-3617 Decently priced, with an extensive menu, this Thai restaurant serves authentic dishes that could fulfill any kind of mood you're in. They also allow you to choose your level of spiciness!
Shanghai East, 105 W. 25th Ave, (650) 522-9098. Tasty Chinese food at very affordable prices. Great dumplings and noodles, and the best Mongolian Beef around.
Yumi Yogurt, 3955 S El Camino Real (650) 341-0939. Amazing flavors of soft serve frozen yogurt and a huge topping bar. Also serve hand scooped ice cream.
Little Shanghai, 17 E. 25th Ave, ☎ 650-573-7161, . Cheap, authentic Shanghainese place. Always seems to be filled with local Chinese families getting their fill.$$. edit
San Mateo has a large Japanese community, and has a number of Japanese restaurants. A few that stand out are:
Santa Ramen 1944 S El Camino Real. Formerly one of the most popular ramen restaurants in the Peninsula, ranked by many as the best, but in the past two years (2011 and 2012) it has ceded the popularity crown to Ramen Dojo (see below). The two restaurants are under the same ownership, however, so the crown remains in the family.
Ramen Dojo 805 South B Street. New restaurant by the same owner as Santa Ramen, and these days more popular than the original one. Much smaller than Santa Ramen and harder to get into (people start lining up half an hour before opening time), no reservations taken.
Ramen Parlor 901 South B Street. The newest restaurant by the same owner as Santa Ramen and Ramen Dojo. Just a block away from Ramen Dojo, and (currently) easier to get into.
Himawari 202 2nd Avenue. Another popular ramen shop in San Mateo.
Sushi Sam's 218 East 3rd Avenue. Probably the most highly regarded sushi restaurant in San Mateo. The other candidate is Yuzu (54 37th Avenue).
Hotaru "33 E 3rd Avenue, 650-343-1152 . Authentic Japanese with an excellent all-around menu including sushi and cooked favorites. Very busy for weekday lunches, quieter at other times. Good value for lunch; prices go up on the dinner menu.
Shabuway 145 E 3rd Ave, 650-548-2483 . One of only a few Shabu-shabu restaurants on the Peninsula.
Kaz Teriyaki Grill 71 East 4th Avenue. Very popular corner takeout Japanese food restaurant in Downtown, fairly authentic.
Taquería Pancho Villa, 365 South B Street, (650) 343-4123. The line out the door should give a clue to the quality inside. Well-roasted meats, tacos and real Mexican food made to order, and inexpensive. Their horchata is good, but their smoothies are better (and made with fresh fruit.)
La Cumbre Taquería , 28 N B St (next to the Caltain station) (650) 344-8989, is Pancho Villa's main competition. Excellent, huge burritos.
There are two branches of the Bay Area-wide Celia's family of restaurants, one up in the hills (3190 Campus Dr. (650) 349-0165 ) and one north of downtown on the border with Burlingame (. Both serve excellent home-style California-Mexican food in a comfortable, sit-down atmosphere. Great for families.
Fletch's Hot Dogs, 385 2nd Ave (attached to the Main St parking garage) 650-685-8301  serves incredible house-made Chicago-style hot dogs, Italian beef, sliders and fries. Wonderful food, wonderfully quick and inexpensive. Very limited seating.
Heidi's Pies, 1941 S. El Camino Real, 650-574-0505  is a local diner; solid rather than distinguished food in general... but they're open 24/7/365 and they are by far the best all-night diner on this part of the peninsula.
Jeffrey's Hamburgers, 42 South B Street, 650-348-8698  is regarded by some as the best hamburger places in town, although fans of Jack's Prime(3723 S. El Camino ) would disagree; you can't go wrong with either.
While there are a lot of pizza places in downtown, none of them are very good; most of the local Bay Area chains (Amicis, Mr. Pizza Man, Pizza My Heart) are represented, but for a good New York-style slice you are going to need to drive a few miles south to Speederia (711 Laurel Street in San Carlos), while for decent Chicago-style thick crust you will have to go further (Little Star in San Francisco; Patxhi's in San Francisco or Palo Alto; Zachary's in Oakland/Berkeley/San Ramon)
If you're willing to go outside of downtown, Rainbow Pizza up in the hills (112 De Anza Boulevard #112, (650) 571-1848) serves a delicious California-Greek take on pizza as well as delicious Greek food.
Many of the restaurants in downtown have full bars - good for a pre- or post-movie drink, but many close relatively early and there is not urban nightlife scene to speak of. There are a few local bars (The Swinging Door on 25th, another on Pacific a few blocks south of Hillsdale) and a small nightclub at the Crowne Plaza Hotel in neighboring Foster City .
Residence Inn San Francisco Airport/San Mateo, 2000 Winward Way, (650) 574-4700, Fax: (650) 572-9084, .
San Mateo Marriott San Francisco Airport, 1770 South Amphlett Blvd, (650) 653-6000, Fax: (650) 573-0533, . Located at the corner of two major freeways, great if you're staying in San Mateo to get somewhere else. Nice lobby for hanging out and a 7-11 convenience store just 1 block away for those late night alcohol runs. Interesting pool and exercise room setup as well. Abundant parking, but you have to pay for it (and it's controlled with gates).
Courtyard San Mateo Foster City, 550 Shell Boulevard, Foster City, ☎ 1-650-377-0600, . The newly renovated Courtyard San Mateo Foster City hotel gives you access to the entire Bay Area. Our new state-of-the-art lobby provides greater flexibility and choices for our guests.edit
Stone Villa Inn San Mateo, 2175 South El Camino Real, San Mateo, CA. 94403, ☎ (650) 458-6556, . Located just south of San Francisco, the newly renovated Stone Villa inn of San Mateo is within walking distance to the San Mateo Event Center,College of San Mateo, Oracle, AT&T Communications, Electronic Arts, Visa USA, Visa International and the San Francisco Airport.edit
If you're trying to go north to San Francisco, mass transit is recommended; Caltrain has three stops in San Mateo, although BART (a short drive north at the Millbrae station/terminal) is quicker and will take you to a part of downtown SF more interesting to most tourists.
If you've already visited San Francisco, you can drive east to the East Bay via the San Mateo-Hayward Bay Bridge or further south down US-101 to Silicon Valley.
Some points of interest on the lower Peninsula and in Silicon Valley are reachable by Caltrain as well; notably the downtowns of Palo Alto, Mountain View, and San Jose.